Electrochemically exfoliated graphene-like nanosheets for use in ceramic nanocomposites

ma e ials A icle Elec ochemically Ex olia ed G aphene-Like Nanoshee s o Use in Ce amic Nanocomposi es Rosalía Poya o 1,* , Reyes Ve dugo 2, Ca men Muñoz-Fe ei o 2and Ángela Galla do-López 2 1Ins i u o de Ciencia de Ma e iales de Se illa, ICMS (CSIC-US), Amé ico Vespucio 49, 41092 Se illa, Spain 2Depa amen o de Física de la Ma e ia Condensada, ICMS, CSIC-Uni e sidad de Se illa, Apdo. 1065, 41080 Se illa, Spain; [email p o ec ed] (R.V.); [email p o ec ed] (C.M.-F.); [email p o ec ed] (Á.G.-L.) *Co espondence: [email p o ec ed] Recei ed: 21 May 2020; Accep ed: 4 June 2020; Published: 11 June 2020   Abs ac : In his wo k, he syn hesis o g aphene-like nanoshee s (GNS) by an elec ochemical ex olia ion me hod, hei mic os uc u al cha ac e iza ion and hei pe o mance as ille s in a ce amic ma ix composi e ha e been assessed. To ab ica e he composi es, 3 mol % y ia e agonal zi conia (3YTZP) powde s wi h 1 ol % GNS we e p ocessed by plane a y ball milling in e -bu anol o enhance he GNS dis ibu ion h oughou he ma ix, and densi ied by spa k plasma sin e ing (SPS). Acco ding o a ho ough Raman analysis and SEM obse a ions, he elec ochemically ex olia ed GNS possessed less han 10 g aphene laye s and a la e al size lowe han 1 µ m. Howe e , hey con ained amo phous ca bon and acancy-like de ec s. In con as he GNS in he sin e ed composi e exhibi ed enhanced quali y wi h a lowe numbe o de ec s, and hey we e wa y, semi- anspa en and wi h e y low hickness. The ob ained nanocomposi e was ully dense wi h a homogeneous dis ibu ion o GNS in o he ma ix. The Vicke s ha dness o he nanocomposi e showed simila alues o hose o a monoli hic 3YTZP ce amic sin e ed in he same condi ions, and o he epo ed ones o a 3YTZP composi e wi h he same con en o comme cial g aphene nanoshee s. Keywo ds: g aphene; elec ochemical ex olia ion me hod; 3YTZP; ce amic nanocomposi es; plane a y ball milling; SPS; Raman spec oscopy; elec on mic oscopy; Vicke s inden a ions 1. In oduc ion Since he i s isola ion o single-laye g aphene in 2004 by he mechanical ex olia ion o g aphi e — he “Sco ch ape” me hod [ 1 ]—i s unique p ope ies ha e mo i a ed a con inuous g ow h in esea ch ac i i y. I has been conside ed as a easible candida e o applica ions in uel cells, composi es, elec onic de ices, senso s, and pho ode ec o s [2]. In he las decade, g aphene has mainly been syn hesized using wo di e en app oaches: bo om-up, in which g aphene is g own om small molecula ca bon p ecu so s, and op-down, in which g aphene is ex olia ed om g aphi e as pa en ma e ial [ 2 ]. Among he bo om-up app oaches, he chemical apo deposi ion (CVD) echnique is he mos popula way o deposi ion o g aphene ilms on me al oils o silicon subs a es [ 3 – 5 ]. Toge he wi h epi axial g ow h [ 6 ], hese a e me hods ha allow he o ma ion o high-quali y, la ge a ea g aphene, encou aging i s applica ion in highly lexible and conduc ing ilms. Howe e , hese me hods p esen d awbacks such as high manu ac u ing cos s o he equi emen o sophis ica ed equipmen , high empe a u es and expensi e subs a es [3]. On he o he hand, when op-down app oaches such as mechanochemical syn hesis [ 7 , 8 ] o liquid phase ex olia ion [ 9 , 10 ] a e simple, cos -e ec i e and easily scalable, hey ha e been p esen ed by di e en au ho s such as sui able me hods o g aphene mass p oduc ion [ 7 , 11 ]. The syn hesis o g aphene oxide by he mechanochemical me hod has also been epo ed [ 12 ]. The main disad an age Ma e ials 2020,13, 2656; doi:10.3390/ma13112656 www.mdpi.com/jou nal/ma e ials Ma e ials 2020,13, 2656 2 o 13 o hese echniques is ha he ob ained s uc u es can ha e a g ea e numbe o de ec s han he ones ha o igina e om bo om-up me hods. Elec ochemical ex olia ion has had a s ong impac on he de elopmen o echniques o ob ain g aphene because i p o ides an economical, simple and as way o p oduce i . I is easily ep oducible because i can be pe o med unde en i onmen al condi ions, and oxici y- ee componen s ha can be easily emo ed a e he p ocess a e used. In addi ion, he use o g aphi e as s a ing ma e ial, oge he wi h he good esul s ob ained om his p ocess, educe he cos o p oducing g aphene, esul ing in an e icien and a o dable me hod o he scien i ic communi y [ 13 ]. Mo eo e , some s udies ha e epo ed he p oduc ion o high-quali y hin g aphene shee s wi h la e al sizes up o 30 µ m by elec ochemical ex olia ion o g aphi e [ 10 , 11 , 14 ]. Howe e , when his ype o syn hesis echnique is used, i is no easy o gene a e single-laye g aphene, and g aphene nanoshee s (GNS) a e usually ob ained. Thus, a e he syn hesis s ep, i is essen ial o cha ac e ize he nanos uc u es in o de o assess he la e al dimension, he numbe o g aphene laye s and he possible p esence o de ec s c ea ed du ing he syn hesis p ocess [ 7 , 8 , 10 ]. In ecen yea s, new app oaches o he elec ochemical ex olia ion echnique ha e been sugges ed in o de o imp o e he yield [ 11 , 14 ] and o p omo e he ob aining o mos ly single- and ew-laye g aphene shee s [15]. Among he di e en applica ions o g aphene, i s use as a ille in composi e ma e ials has awakened he in e es o he scien i ic communi y in he las yea s, owing o he ele an p ope ies ha hese nanos uc u es impa o mos ma e ials [ 2 , 16 ]. In he case o ce amics, a s ong in e es has been gene a ed in he de elopmen o ad anced ce amics in which he p esence o g aphene as a second phase imp o es hei ac u e oughness and elec ical conduc i i y [ 17 , 18 ]. Howe e , hese composi e ma e ials p esen a p ocessing challenge due o g aphene’s s ong endency o agglome a e, as a consequence o i s high su ace a ea. This nega i ely a ec s he p ope ies o he composi e, so ad anced p ocessing echniques a e usually needed [ 19 , 20 ]. Among he ad anced ce amics, 3 mol % y ia e agonal zi conia (3YTZP) p esen s a ema kable echnological in e es because o i s excellen mechanical p ope ies, such as Young’s modulus, ac u e oughness and ha dness, as well as i s chemical s abili y [ 21 ]. Recen s udies abou 3YTZP composi es wi h g aphene ha e epo ed enhancemen s on p ope ies as ac u e oughness o lexu e s eng h o e y low addi ions o g aphene nanos uc u es [22,23]. Mos o he published s udies abou g aphene-ce amic composi es gene ally use comme cially acqui ed g aphene nanoshee s. Al hough p omising esul s in e ms o enhancemen o mechanical and elec ical p ope ies ha e been epo ed o composi es wi h cos -e ec i e g aphene nanopla ele s p epa ed using ad anced powde p ocessing echniques [ 20 , 23 ], he bes esul s ha e been ob ained in composi es wi h hinne and mo e expensi e g aphene nanoshee s o ew-laye g aphene [ 24 – 26 ]. This could hinde he indus ial applica ion o hese composi e ma e ials due o he high manu ac u ing cos s. In his con ex , he sea ch o cos -e ec i e syn hesis echniques o ob ain g aphene nanoshee s o i s applica ion in ce amic nanocomposi es is e y necessa y. In his wo k, he syn hesis o g aphene-like nanoshee s has been assessed by means o a simple, cos -e ec i e and as elec ochemical ex olia ion echnique, using g aphi e as pa en ma e ial. A e a de ailed cha ac e iza ion o he as-syn hesized nanoshee s by Raman spec oscopy and elec on mic oscopy obse a ions, hey we e inco po a ed as ille in a 3YTZP ma ix nanocomposi e. Powde s wi h 1 ol % GNS we e p ocessed by plane a y ball milling in e -bu anol o enhance he GNS dis ibu ion h oughou he ma ix, and densi ied by spa k plasma sin e ing (SPS). The quali y and le el o de ec s o he GNS in he composi e we e assessed by Raman spec oscopy. The mic os uc u e and ha dness o he ob ained nanocomposi e was analyzed and compa ed o he epo ed ones o 3YTZP composi es p epa ed wi h comme cial nanoshee s. Ma e ials 2020,13, 2656 3 o 13 2. Ma e ials and Me hods 2.1. G aphene Syn hesis and Cha ac e iza ion The g aphene-like nanoshee s we e ob ained by he elec ochemical ex olia ion me hod [ 10 ], using a g aphi e ba (1 cm diame e , 10 cm long, Good ellow Camb idge L d., Hun ingdon, UK) and a pla inum wi e ac ing as anode and ca hode, espec i ely. The ionic solu ion was p epa ed by aking 1.3 mL o sulphu ic acid (95–98%, Pan eac, Cas ella del Vall è s, Spain) and dilu ing in 100 mL o DI wa e . The pla inum wi e and he g aphi e ba we e imme sed in o he ionic solu ion wi h a sepa a ion o 5 cm, and he elec ochemical ex olia ion p ocess was ca ied ou by applying DC bias om 1 o 10 V, wi h s eps o 1 V e e y en minu es du ing a o al ime o 1.5 h. A e his ime, 10 V we e applied o 30 min. Con inuous magne ic agi a ion was applied du ing he whole ex olia ion p ocess. A e he ex olia ion p ocess, he suspensions we e washed wi h DI wa e and isop opyl alcohol by acuum il a ion using 200 nm po e il e alumina memb anes (Wha man, Maids one, UK) and cen i uged (model SIGMA 3-30KS, Sigma Labo a o y Cen i uges, Os e ode am Ha z, Ge many) a 8500 .p.m. o 15 min o emo e g aphi e agg ega es. The suspensions we e ozen wi h liquid ni ogen and eeze-d ied o 48 h a − 80 ◦ C in o de o a oid e-agglome a ion o he ob ained nanoshee s du ing d ying (C yodos-80, Tels a , Te asa, Spain). Raman spec oscopy and high- esolu ion scanning elec on mic oscopy (HRSEM, S5200, Hi achi High-Technologies Co p., Tokyo, Japan) we e used o cha ac e ize he numbe o laye s, mo phology and size dis ibu ion o he as-syn hesized GNS. To ha end, a ew d ople s o GNS suspension in isop opyl alcohol we e deposi ed on a glass slide o Raman spec oscopy o on a Cu ansmission g id wi h C coa ing o HRSEM inspec ion a e d ying. A leas 10 Raman spec a we e acqui ed on he elec ochemically ex olia ed GNS using a dispe si e mic oscope Raman Ho iba Jobin Y on LabRam HR800 (ICMS), wi h a g een lase He-Ne (532.1 nm) a 20 mW. The i s -o de ( om 1000 o 2000 cm −1 ) Raman spec a we e i ed o a sum o i e unc ions: wo Gaussian and h ee pseudo-Voig unc ions. In he second-o de spec a ( om 2250 o 3300 cm −1 ) h ee Lo en z and h ee pseudo-Voig unc ions we e used. The i s we e ca ied ou using he O iginLab so wa e (O iginP o 2019, O iginLab Co po a ion, No hamp on, MA, USA). 2.2. Nanocomposi e P ocessing and Cha ac e iza ion Composi e powde s wi h 1 ol % GNS we e p epa ed using he elec ochemically ex olia ed nanoshee s and comme cial 3YTZP powde s (40 nm pa icle size, TZ-3YB-E, Tosoh Eu ope B.V, Ams e dam, The Ne he lands), which we e p e iously annealed a 850 ◦ C o 30 min in ai . Plane a y ball milling (Pul e ise e 7 classic line, F i sch, Ida -Obe s ein, Ge many) was used o homogenize he powde s in a 10 w/w% e -bu anol ( -BuOH)/wa e mix u e a 700 .p.m. o 15 min. A 45 mL zi conia ja and se en 15 mm diame e zi conia balls we e used. A e d ying on a o a y e apo a o , he composi e powde s we e homogenized in an aga ha mo a and spa k plasma sin e ed a 1250 ◦ C o 5 min, wi h an applied p essu e o 75 MPa and hea ing and cooling amps o 300 and 50 ◦ C/min, espec i ely (SPS model 515 S, D . Sin e , Inc., Kanagawa, Japan). A shee o g aphi e pape was placed be ween he powde s and he die/punches o bo h ensu e hei elec ical, mechanical and he mal con ac and also o an easy emo al. The empe a u e was con inually moni o ed by means o an op ical py ome e ocused on he side o he g aphi e die. Cylind ical samples wi h 10 mm diame e and 2 mm hickness we e ob ained. The su ace g aphi e pape om he SPS molding sys em was manually elimina ed by g inding. Toaccoun o possibles uc u almodi ica ions o he g aphene-likenanoshee s a e he composi e powde p ocessing and sin e ing, a leas en Raman spec a we e acqui ed on he ob ained powde s a e plane a y ball milling, and on he ac u e su ace o he sin e ed composi e. The i s - and second-o de Raman spec a we e i ed o he unc ions desc ibed in Sec ion 2.1. The densi y o he composi e was de e mined wi h he A chimedes’ me hod using dis illed wa e as he imme sion medium. The heo e ical densi y was calcula ed by he ule o mix u es aking he densi y o he 3YTZP Ma e ials 2020,13, 2656 4 o 13 and he GNS as 6.05 g/cm 3 and 2.2 g/cm 3 , espec i ely. Scanning elec on mic oscopy (SEM) using backsca e ed elec ons (BSE) o imaging (FEI-Teneo, FEI, The mo Fishe , Camb idge, MA, USA) was used o analyze he dispe sion o he GNS in he ce amic ma ix. This mic oscope has wo in-lens de ec o s which allow ob aining high esolu ion images a sho wo k dis ances. Polished in-plane (i.p.) and c oss-sec ion (c.s.) su aces we e analyzed o accoun o he exis ence o any s uc u al aniso opy on he composi e. The g ain size o he ce amic ma ix was es ima ed om SEM images acqui ed on polished c.s. su aces p e iously annealed in ai o 15 min a 1150 ◦ C. The plana equi alen diame e , d=2(a ea/ π ) 1/2 , namely he diame e co esponding o a ci cle wi h he same a ea as he measu ed g ain, was aken as a measu e o he g ain size, a e aging 200 o 300 g ains, acco ding o UNE-EN ISO 13383-1:2016 s anda d. The so wa e packages ImageJ and O iginLab we e used o de e mine he ele an pa ame e s. The ac u e su ace o he composi e was also examined by HRSEM (HRSEM, S5200, Hi achi High-Technologies Co p., Tokyo, Japan). The ha dness o he nanocomposi e was es ima ed om s anda d Vicke s mic o-inden a ions (Vicke s Du amin inden e , S ue s, Copenhagen, Denma k) pe o med on he mi o polished i.p. and c.s. su aces. These wo o ien a ions we e e alua ed o accoun o any possible aniso opy e ec s. Ten inden a ions we e pe o med on each su ace wi h 1.96 N applied load du ing 10 s. The ha dness alues we e calcula ed ollowing he equa ion: H V (GPa) =1854.4 P/D 2 , whe e P is he applied load in N and D he a e age diagonal o he imp in in µm. 3. Resul s and Discussion 3.1. Mic os uc u al Cha ac e iza ion o he G aphene Nanoshee s Typical HRSEM mic og aphs (acqui ed in Seconda y Elec on Image mode) o he elec ochemically ex olia ed nanoshee s a e shown in Figu e 1. I can be obse ed ha some nanoshee s p esen a la e al size lowe ha 1 µ m (Figu e 1a). Howe e , hey show a s ong endency o agglome a e (Figu e 1b), esul ing in GNS in e connec ions wi h a la e al size o se e al mic ons. Ma e ials2020,13,xFORPEERREVIEW4o 14 imagesacqui edonpolishedc.s.su acesp e iouslyannealedinai  o 15mina 1150°C.Theplana  equi alen diame e ,d=2(a ea/π)1/2,namely hediame e co esponding oaci clewi h hesame a eaas hemeasu edg ain,was akenasameasu eo  heg ainsize,a e aging200 o300g ains, acco ding oUNE‐ENISO13383‐1:2016s anda d.Theso wa epackagesImageJandO iginLabwe e used ode e mine he ele an pa ame e s.The ac u esu aceo  hecomposi ewasalsoexamined byHRSEM(HRSEM,S5200,Hi achiHigh‐TechnologiesCo p.,Tokyo,Japan). Theha dnesso  henanocomposi ewases ima ed oms anda dVicke smic o‐inden a ions (Vicke sDu amininden e ,S ue s,Copenhagen,Denma k)pe o medon hemi o polishedi.p. andc.s.su aces.These woo ien a ionswe ee alua ed oaccoun  o anypossibleaniso opy e ec s.Teninden a ionswe epe o medoneachsu acewi h1.96Nappliedloaddu ing10s.The ha dness alueswe ecalcula ed ollowing heequa ion:HV(GPa)=1854.4P/D2,whe ePis he appliedloadinNandD hea e agediagonalo  heimp in inμm. 3.Resul sandDiscussion 3.1.Mic os uc u alCha ac e iza iono  heG apheneNanoshee s TypicalHRSEMmic og aphs(acqui edinSeconda yElec onImagemode) o  he elec ochemicallyex olia ednanoshee sa eshowninFigu e1.I canbeobse ed ha some nanoshee sp esen ala e alsizelowe  ha 1μm(Figu e1a).Howe e , heyshowas ong endency oagglome a e(Figu e1b), esul inginGNSin e connec ionswi hala e alsizeo se e almic ons.  Figu e1.High‐ esolu ionscanningelec onmic oscopy(HRSEM)images o  heelec ochemically ex olia edg aphenenanoshee s,d op‐cas edonaCu ansmissiong id(a)Isola ednanoshee s;(b) agglome a ednanoshee s. TheRamanspec umacqui edon heas‐ex olia ednanoshee sisp esen edinFigu e2a.I is e ysimila  o hedesc ibedonesindi e en wo ks o g aphenenanoshee s, ew‐laye g apheneo  educedg apheneoxide( GO)[10,25,27].The ypicalbandsdesc ibedinli e a u e o  hese nanoma e ialsa eclea lyobse eda ~1350(D),~1585(G)and~2700(2D)cm−1.TheGand2Dbands a ealways oundinp is ineg aphene.TheGbandisdue o hedoublydegene a ezonecen e E2g modeand he2Dbandis hesecondo de o zone‐bounda yphonons[28–30].On heo he hand, heDbandis hemos p ominen o  hede ec ‐inducedbands.I hasbeen epo ed ha  hesebands a ise omb ea hing‐likemodeso  heca bon ingsac i a edbyde ec s iadouble‐ esonanceRaman p ocess[28–30].Usually, heID/IGin ensi y a ioisanindica i eo  hep esenceo de ec son he g aphenela ice[18,31,32]. Alongwi h hepeaks ha a eclea lyobse edin hespec um,o he de ec ‐inducedbandsa e p esen a ~1100–1200and~1610–1620cm−1.Thesebandsa ede ec edinFigu e2aasapeak ha  o e lapswi h hele sideo  heDbandandasashoulde on he igh sideo  heGpeak, espec i ely. While hela e hasbeennamedinmos o  hepublishedwo ksasD’, he o me hasbeennamedas T1[33],D4[34],D*[23,27,35]o D’’[29,30,36]dependingon heau ho sandon hes udiedca bon‐ Figu e 1. High- esolu ion scanning elec on mic oscopy (HRSEM) images o he elec ochemically ex olia ed g aphene nanoshee s, d op-cas ed on a Cu ansmission g id ( a ) Isola ed nanoshee s; (b) agglome a ed nanoshee s. The Raman spec um acqui ed on he as-ex olia ed nanoshee s is p esen ed in Figu e 2a. I is e y simila o he desc ibed ones in di e en wo ks o g aphene nanoshee s, ew-laye g aphene o educed g aphene oxide ( GO) [ 10 , 25 , 27 ]. The ypical bands desc ibed in li e a u e o hese nanoma e ials a e clea ly obse ed a ~1350 (D), ~1585 (G) and ~2700 (2D) cm −1 . The G and 2D bands a e always ound in p is ine g aphene. The G band is due o he doubly degene a e zone cen e E2g mode and he 2D band is he second o de o zone-bounda y phonons [ 28 – 30 ]. On he o he hand, he D band is he mos p ominen o he de ec -induced bands. I has been epo ed ha hese bands a ise om b ea hing-like Ma e ials 2020,13, 2656 5 o 13 modes o he ca bon ings ac i a ed by de ec s ia double- esonance Raman p ocess [ 28 – 30 ]. Usually, he ID/IGin ensi y a io is an indica i e o he p esence o de ec s on he g aphene la ice [18,31,32]. Ma e ials2020,13,xFORPEERREVIEW5o 14 basedma e ial.Mo eo e ,ab oadshoulde be ween heDandGpeakscanalsobeseeninFigu e 2a.This ea u ehasbeen ela ed oaRamanbanda ~1500cm−1inde ec edca bon‐basedma e ials, andhasbeennamedasT2[33],D3[34,37]o D’’[27,35]bydi e en au ho s.Thisbandhasbeen ela ed o hep esenceo amo phousca boning apheneoxide[27,35],ca bonnano ubes[33]o  o he ca bon‐basedma e ials[34].In hep esen wo k,wewillassume henomencla u eD‘’,D3and D’ o  hebandsloca eda ~1100–1200,~1500and~1610–1620cm−1, espec i ely. Usually, heD‘’,D3andD’bandsa eno desc ibedwhenanalyzing heRamanspec ao  g aphene‐basednanoma e ialsbecause heya e e yweakpeaks.Ne e heless,when hesebands p esen a ema kablein ensi y, heyappea  oo e lapwi h heDandGpeaks.Thismakes he decon olu iono  he i s ‐o de spec um( om1000 o2000cm−1)essen ial o  heco ec  in e p e a iono  heRamanspec um,asi issugges edbydi e en au ho s[27,33,35,38,39].The i ingso  he i s ‐andsecond‐o de spec aallow hesui ableob ainingo  heposi ion,in ensi y (in eg a eda ea)andbandwid ho  hedi e en peaks.Thesepa ame e sallowus oes ablish he p esenceandna u eo de ec sin heelec ochemicallyex olia ednanoshee s. Figu e2b,cshowexampleso  he i ings ha ha ebeenca iedou  o all heRamanspec a acqui edon heelec ochemicallyex olia edg aphenenanoshee s,using woGaussian(D‘’andD3) and h eepseudo‐Voig (D,GandD’) unc ions o  he i s ‐o de spec a,and h eeLo en z(2D) and h eepseudo‐Voig (D+D*,D+D’and2D´) unc ions o  hesecond‐o de spec a.  1000 1200 1400 1600 1800 In ensi y (a.u.) Raman shi (cm -1 ) expe imen al da a i da a D'' D D 3 G D' D D 3 D' G D'' (b) 1000 1500 2000 2500 3000 D+D' 2D G In ensi y (a.u.) Raman shi (cm -1 ) (a) D'' D Ma e ials2020,13,xFORPEERREVIEW6o 14 Figu e2.(a)Ramanspec umacqui edon heas‐syn hesizedg aphenenanoshee s;(b) Decon olu iono  he i s ‐o de Ramanspec umusing i e unc ions(D‘’,D,D3,GandD’bands); (c)Decon olu iono  hesecond‐o de Ramanspec umusingsix unc ions(D+D*,2D1,2D2,2D3,D +D’and2D’bands). Thehigh alueso  heID/IGandID’/IG a ios(Table1)poin  o heexis enceo de ec sanddiso de  in heex olia ednanoshee s.Mo eo e , helow alueo I2D/IGsuppo s hisconclusion,asi hasbeen published ha  he2Dbando highlydiso de edg aphene educesi sin ensi yandinc easesi s wid h[27,31].Ne e heless,acco ding o he e minologyin oducedbyFe a ie al.[29] ega ding heRamanspec ao diso de edg aphene, heelec ochemicallyex olia ednanoshee sob ainedin hep esen wo kwouldco espond olow‐de ec g aphene(s ageIin heclassi ica ionp oposedby heseau ho s).Theyes ablisheda ansi ionbe weens agesI(low‐de ec g aphene)andII (diso de edg aphene)a ID/IG=3.5,and hein ensi y a ioo  heob ainedGNSislowe  han his alue(2.24±0.05).Theexis enceo ap onouncedD3band(see hehigh alueo  heID3/IG a ioob ained a e  i ing,Table1)isa ibu ed o hep esenceo amo phousca bonin henanoshee s,as sugges edbyp e iousau ho s[27,34,35]. Table1.In ensi y a ioso  heD,D3,D’and2Dbandswi h espec  o heGpeak,ob ained o  heas‐ syn hesizedg aphene‐likenanoshee s(GNS)and heGNSin hesin e edcomposi ea e  i ing he i s ‐andsecond‐o de Ramanspec a. SampleID / IGID3 / IGIDʹ / IGI2D / IG As‐syn hesizedGNS2.24±0.050.485±0.0210.23±0.070.219±0.011 Sin e ed1 ol%GNS/3YTZP1.93±0.060.249±0.0210.18±0.070.46±0.05 Theshapeo  hesecond‐o de spec um(Figu e2c)—wi haD+D’bandwi hhighin ensi y—is e ysimila  o he epo edone o monolaye g aphenebomba dedbylow‐ene gya gonionsin o de  oinducediso de in hesys em[31].I hasbeenshown ha  hisionbomba dmen p omo es acancy‐ ypede ec s[31,32],so hediso de de ec edon heex olia ednanoshee sis e ylikely causedby acancy‐likede ec s. Finally, he i ingo  he2Dbandcouldbeca iedou using h eeLo en zian unc ions(Figu e 2c), e ealing ha  heGNSp esen anumbe o laye slowe  han10,acco ding oFe a ie al.[28] andMala de al.[40].Thus, heelec ochemicalex olia ion echniqueusedin hiswo kallows he p oduc iono g aphene‐likenanoshee s: educedg apheneoxideo  ew‐laye edde ec edg aphene.  2400 2600 2800 3000 3200 In ensi y (a.u.) Raman shi (cm -1 ) expe imen al da a i da a D+D* 2D 1 2D 2 2D 3 D+D' 2D' (c) D+D* D+D' 2D' Figu e 2. ( a ) Raman spec um acqui ed on he as-syn hesized g aphene nanoshee s; ( b ) Decon olu ion o he i s -o de Raman spec um using i e unc ions (D‘’, D, D 3 , G and D’ bands); ( c ) Decon olu ion o he second-o de Raman spec um using six unc ions (D +D*, 2D 1 , 2D 2 , 2D 3 , D +D’ and 2D’ bands). Along wi h he peaks ha a e clea ly obse ed in he spec um, o he de ec -induced bands a e p esen a ~1100–1200 and ~1610–1620 cm −1 . These bands a e de ec ed in Figu e 2a as a peak ha o e laps wi h he le side o he D band and as a shoulde on he igh side o he G peak, espec i ely. While he la e has been named in mos o he published wo ks as D’, he o me has been named as T 1 [ 33 ], D 4 [ 34 ], D* [ 23 , 27 , 35 ] o D” [ 29 , 30 , 36 ] depending on he au ho s and on he s udied ca bon-based ma e ial. Mo eo e , a b oad shoulde be ween he D and G peaks can also be seen in Figu e 2a. This ea u e has been ela ed o a Raman band a ~1500 cm −1 in de ec ed ca bon-based ma e ials, and has been named as T 2 [ 33 ], D 3 [ 34 , 37 ] o D” [ 27 , 35 ] by di e en au ho s. This band has been ela ed o he p esence o amo phous ca bon in g aphene oxide [ 27 , 35 ], ca bon nano ubes [ 33 ] o o he ca bon-based ma e ials [ 34 ]. In he p esen wo k, we will assume he nomencla u e D‘’, D 3 and D’ o he bands loca ed a ~1100–1200, ~1500 and ~1610–1620 cm−1, espec i ely. Usually, he D‘’, D 3 and D’ bands a e no desc ibed when analyzing he Raman spec a o g aphene-based nanoma e ials because hey a e e y weak peaks. Ne e heless, when hese bands p esen a ema kable in ensi y, hey appea o o e lap wi h he D and G peaks. This makes he decon olu iono he i s -o de spec um( om1000 o 2000cm −1 )essen ial o he co ec in e p e a ion Ma e ials 2020,13, 2656 6 o 13 o he Raman spec um, as i is sugges ed by di e en au ho s [ 27 , 33 , 35 , 38 , 39 ]. The i ings o he i s - and second-o de spec a allow he sui able ob aining o he posi ion, in ensi y (in eg a ed a ea) and band wid h o he di e en peaks. These pa ame e s allow us o es ablish he p esence and na u e o de ec s in he elec ochemically ex olia ed nanoshee s. Figu e 2b,c show examples o he i ings ha ha e been ca ied ou o all he Raman spec a acqui ed on he elec ochemically ex olia ed g aphene nanoshee s, using wo Gaussian (D‘’ and D 3 ) and h ee pseudo-Voig (D, G and D’) unc ions o he i s -o de spec a, and h ee Lo en z (2D) and h ee pseudo-Voig (D +D*, D +D’ and 2D´) unc ions o he second-o de spec a. The high alues o he I D /I G and I D’ /I G a ios (Table 1) poin o he exis ence o de ec s and diso de in he ex olia ed nanoshee s. Mo eo e , he low alue o I 2D /I G suppo s his conclusion, as i has been published ha he 2D band o highly diso de ed g aphene educes i s in ensi y and inc eases i s wid h [ 27 , 31 ]. Ne e heless, acco ding o he e minology in oduced by Fe a i e al. [ 29 ] ega ding he Raman spec a o diso de ed g aphene, he elec ochemically ex olia ed nanoshee s ob ained in he p esen wo k would co espond o low-de ec g aphene (s age I in he classi ica ion p oposed by hese au ho s). They es ablished a ansi ion be ween s ages I (low-de ec g aphene) and II (diso de ed g aphene) a I D /I G =3.5, and he in ensi y a io o he ob ained GNS is lowe han his alue (2.24 ±0.05). The exis ence o a p onounced D3band (see he high alue o he ID3/IG a io ob ained a e i ing, Table 1) is a ibu ed o he p esence o amo phous ca bon in he nanoshee s, as sugges ed by p e ious au ho s [27,34,35]. Table 1. In ensi y a ios o he D, D 3 , D’ and 2D bands wi h espec o he G peak, ob ained o he as-syn hesized g aphene-like nanoshee s (GNS) and he GNS in he sin e ed composi e a e i ing he i s - and second-o de Raman spec a. Sample ID/IGID3/IGID’/IGI2D/IG As-syn hesized GNS 2.24 ±0.05 0.485 ±0.021 0.23 ±0.07 0.219 ±0.011 Sin e ed 1 ol % GNS/3YTZP 1.93 ±0.06 0.249 ±0.021 0.18 ±0.07 0.46 ±0.05 The shape o he second-o de spec um (Figu e 2c)—wi h a D+D’ band wi h high in ensi y—is e y simila o he epo ed one o monolaye g aphene bomba ded by low-ene gy a gon ions in o de o induce diso de in he sys em [ 31 ]. I has been shown ha his ion bomba dmen p omo es acancy- ype de ec s [ 31 , 32 ], so he diso de de ec ed on he ex olia ed nanoshee s is e y likely caused by acancy-like de ec s. Finally, he i ing o he 2D band could be ca ied ou using h ee Lo en zian unc ions (Figu e 2c), e ealing ha he GNS p esen a numbe o laye s lowe han 10, acco ding o Fe a i e al. [ 28 ] and Mala d e al. [ 40 ]. Thus, he elec ochemical ex olia ion echnique used in his wo k allows he p oduc ion o g aphene-like nanoshee s: educed g aphene oxide o ew-laye ed de ec ed g aphene. 3.2. Mic os uc u al Cha ac e iza ion o he Nanocomposi e A ela i e densi y o 99% was ob ained o he sin e ed composi e. This high-densi y alue e eals he achie emen o a high le el o compac ion and low po osi y in he composi e, as i is suppo ed by he SEM mic og aphs o he composi e polished su aces annealed in ai (Figu e 3), whe e po es a e no dis inguished. I is possible o obse e some oids closed o he ce amic g ains; howe e , hei size is e y simila o ha o he g ains, which poin s o he ac ha hey a e he consequence o g ain pull-ou du ing he g inding and polishing s eps p e ious o he annealing. The ull densi ica ion o his ype o composi es has been p e iously epo ed o composi es wi h simila con en s o o he ypes o comme cial g aphene-based nanoma e ials, p epa ed wi h simila p ocessing and sin e ing ou ines [23,41]. Ma e ials 2020,13, 2656 7 o 13 Ma e ials2020,13,xFORPEERREVIEW7o 14 3.2.Mic os uc u alCha ac e iza iono  heNanocomposi e A ela i edensi yo 99%wasob ained o  hesin e edcomposi e.Thishigh‐densi y alue e eals heachie emen o ahighle elo compac ionandlowpo osi yin hecomposi e,asi is suppo edby heSEMmic og aphso  hecomposi epolishedsu acesannealedinai (Figu e3), whe epo esa eno dis inguished.I ispossible oobse esome oidsclosed o hece amicg ains; howe e , hei sizeis e ysimila  o ha o  heg ains,whichpoin s o he ac  ha  heya e he consequenceo g ainpull‐ou du ing heg indingandpolishings epsp e ious o heannealing.The ulldensi ica iono  his ypeo composi eshasbeenp e iously epo ed o composi eswi hsimila  con en so o he  ypeso comme cialg aphene‐basednanoma e ials,p epa edwi hsimila  p ocessingandsin e ing ou ines[23,41].  Figu e3.SEMmic og apho  hepolishedc.s.su aceo  he3YTZPcomposi ea e annealinginai . Ag ainsizeo 0.17±0.09μmhasbeenob ained o  henanocomposi e, e ealingag ain e inemen wi h espec  oamonoli hic3YTZPce amicsin e edusing hesamecondi ions(0.29± 0.02μm[41]),inag eemen wi h heg aing ow hinhibi ione ec p e iously epo ed o ce amic composi eswi hcomme cialg aphene‐basednanoma e ials[19,23,25,41].Theg ain e inemen  shownby hecomposi ein hiswo kismo e ema kable han he epo edonesinp e iouswo ks o 3YTZPcomposi eswi h hesamecon en o comme cialg aphenenanopla ele s[41](0.27μm) andg aphenenanoshee sob ainedbymechanicalex olia iono comme cialGNP[23](0.25μm).This couldbe ela ed o heop imumGNSdis ibu ion h oughou  hema ixachie edin hiswo k.This isaconsequence,on heonehand,o  helowdimensionso  heelec ochemicallyex olia edGNS, and,on heo he hand,o  headequa euseo ad ancedpowde p ocessingandsin e ing echniques. TheRamanspec ao  hecomposi epowde a e plane a yballmillingando  hesin e ed ce amiccomposi ea ep esen edinFigu e4a.Thecha ac e is icpeaks o g aphenea eclea ly obse ed, e ealing ha nei he  hehigh‐ene gymillingdu ingpowde p ocessingno  hehigh empe a u edu ingsin e ingdeg aded heelec ochemicallyex olia edGNS.Howe e ,apeakwi h highin ensi ywasde ec eda ~1000cm−1,whichhadno beenobse edin hespec umo  heas‐ ex olia edGNS(Figu e2a).Ino de  oanalyze heo igino  hispeak, heRamanspec awe e acqui edinanex ended equency ange(inse inFigu e4a) e ealing heexis enceo mul iplepeaks. Toge he wi h hepeaksco esponding o he e agonal(264,320,460,643cm−1)andmonoclinic(365, 488cm−1)phaseso  hezi coniama ix[42],sha ppeaksin he ange~500–630cm−1andab oadband in he ange~700–1100cm−1we e ound.Thesebandscanbea ibu ed o hep esenceo alow pe cen ageo analumino‐silica e(AS)glass[43] ha couldha ebeenin oducedascon amina ion in o hecomposi epowde du ing hehigh‐ene gyballmilling.Thepe cen ageo  hisphasemus be signi ican lylow,asi wasno de ec edbyX‐ aydi ac ion( esul sno shown).Howe e , u u e e o swillbeca iedou  omodi y heplane a yballmillingcondi ionsino de  oa oid he o ma iono  his aceo ASglass.Ino de  ope o m hedecon olu iono  he i s ‐o de spec a o sui ablyanalyze hede ec ‐ ela edpeaksand hein ensi y a ios,wein oducedanewpeak—a  ~1000cm−1— o he i ings. Figu e 3. SEM mic og aph o he polished c. s. su ace o he 3YTZP composi e a e annealing in ai . A g ain size o 0.17 ± 0.09 µ m has been ob ained o he nanocomposi e, e ealing a g ain e inemen wi h espec o a monoli hic 3YTZP ce amic sin e ed using he same condi ions (0.29 ± 0.02 µ m [ 41 ]), in ag eemen wi h he g ain g ow h inhibi ion e ec p e iously epo ed o ce amic composi es wi h comme cial g aphene-based nanoma e ials [ 19 , 23 , 25 , 41 ]. The g ain e inemen shown by he composi e in his wo k is mo e ema kable han he epo ed ones in p e ious wo ks o 3YTZP composi es wi h he same con en o comme cial g aphene nanopla ele s [ 41 ] (0.27 µ m) and g aphene nanoshee s ob ained by mechanical ex olia ion o comme cial GNP [ 23 ] (0.25 µ m). This could be ela ed o he op imum GNS dis ibu ion h oughou he ma ix achie ed in his wo k. This is a consequence, on he one hand, o he low dimensions o he elec ochemically ex olia ed GNS, and, on he o he hand, o he adequa e use o ad anced powde p ocessing and sin e ing echniques. The Raman spec a o he composi e powde a e plane a y ball milling and o he sin e ed ce amic composi e a e p esen ed in Figu e 4a. The cha ac e is ic peaks o g aphene a e clea ly obse ed, e ealing ha nei he he high-ene gy milling du ing powde p ocessing no he high empe a u e du ing sin e ing deg aded he elec ochemically ex olia ed GNS. Howe e , a peak wi h high in ensi y was de ec ed a ~1000 cm −1 , which had no been obse ed in he spec um o he as-ex olia ed GNS (Figu e 2a). In o de o analyze he o igin o his peak, he Raman spec a we e acqui ed in an ex ended equency ange (inse in Figu e 4a) e ealing he exis ence o mul iple peaks. Toge he wi h he peaks co esponding o he e agonal (264, 320, 460, 643 cm −1 ) and monoclinic (365, 488 cm −1 ) phases o he zi conia ma ix [ 42 ], sha p peaks in he ange ~500–630 cm −1 and a b oad band in he ange ~700–1100 cm −1 we e ound. These bands can be a ibu ed o he p esence o a low pe cen age o an alumino-silica e (AS) glass [ 43 ] ha could ha e been in oduced as con amina ion in o he composi e powde du ing he high-ene gy ball milling. The pe cen age o his phase mus be signi ican ly low, as i was no de ec ed by X- ay di ac ion ( esul s no shown). Howe e , u u e e o s will be ca ied ou o modi y he plane a y ball milling condi ions in o de o a oid he o ma ion o his ace o AS glass. In o de o pe o m he decon olu ion o he i s -o de spec a o sui ably analyze he de ec - ela ed peaks and he in ensi y a ios, we in oduced a new peak—a ~1000 cm−1— o he i ings. Figu e 4b,c shows examples o he i ings ha ha e been ca ied ou o all he Raman spec a acqui ed on he sin e ed ce amic composi e using wo Gaussian (D” and D 3 ) and ou pseudo-Voig (AS glass, D, G and D’) unc ions o he i s -o de spec a, and h ee Lo en z (2D) and h ee pseudo-Voig (D +D*, D +D’ and 2D´) unc ions o he second-o de spec a. A dec ease o he de ec - ela ed D and D’ peaks in ensi y, along wi h an inc ease o he in ensi y o he 2D band, is obse ed o he GNS in he sin e ed composi e, in compa ison wi h he as-ex olia ed GNS (Table 1). Also, a dec ease o he D 3 band is ound, poin ing o a lowe amoun o amo phous ca bon in he GNS a e sin e ing, in ag eemen wi h published esul s ha he I D3 /I G a io dec eases as he c ys allini y inc eases [ 27 ]. All o his e eals a dec ease o he numbe o de ec s and a es o a ion o he g aphene ne wo k du ing he high- empe a u e sin e ing p ocess [27,31,32,39]. Ma e ials 2020,13, 2656 8 o 13 Ma e ials2020,13,xFORPEERREVIEW8o 14 Figu e4.(a)Ramanspec aacqui edon hecomposi epowde sa e high‐ene gyplane a yball millingandon hesin e edcomposi e,inse :de ailo  heRamanspec umacqui edon hesin e ed composi ein he ange150–1800cm−1;(b)Decon olu iono  he i s ‐o de Ramanspec umo  he sin e edcomposi e;(c)Decon olu iono  hesecond‐o de Ramanspec umo  hesin e edcomposi e (D+D*,2D1,2D2,2D3,D+D’and2D’bands). Figu e4b,cshowsexampleso  he i ings ha ha ebeenca iedou  o all heRamanspec a acqui edon hesin e edce amiccomposi eusing woGaussian(D’’andD3)and ou pseudo‐Voig  (ASglass,D,GandD’) unc ions o  he i s ‐o de spec a,and h eeLo en z(2D)and h eepseudo‐ Voig (D+D*,D+D’and2D´) unc ions o  hesecond‐o de spec a. Adec easeo  hede ec ‐ ela edDandD’peaksin ensi y,alongwi haninc easeo  hein ensi y o  he2Dband,isobse ed o  heGNSin hesin e edcomposi e,incompa isonwi h heas‐ ex olia edGNS(Table1).Also,adec easeo  heD3bandis ound,poin ing oalowe amoun o  amo phousca bonin heGNSa e sin e ing,inag eemen wi hpublished esul s ha  heID3/IG a io dec easesas hec ys allini yinc eases[27].Allo  his e ealsadec easeo  henumbe o de ec sand a es o a iono  heg aphenene wo kdu ing hehigh‐ empe a u esin e ingp ocess[27,31,32,39]. Ano he pa ame e  ha cangi ein o ma ionabou de ec sing apheneis hebandwid h o D, G,D’and2Dbands,as hei wid hsinc easewi hag owingnumbe o de ec s[31].Ma insFe ei a e al.[31]ha e epo ed ha  hewid ho GandD’peaksha ealessp onounceddependence han heDand2Dbands.Acco ding o hisassessmen , hebandwid hso  heGandD’peakss ay in a iableinbo h heas‐ex olia edGNSand hesin e edcomposi e(Table2),whilealowe Dband 1000 1200 1400 1600 1800 In ensi y (a.u.) Raman shi (cm -1 ) expe imen al da a i da a AS glass D'' D D 3 G D D'' D D 3 G D' (b) 2400 2600 2800 3000 3200 In ensi y (a.u.) Raman shi (cm -1 ) expe imen al da a i da a D+D* 2D 1 2D 2 2D 3 D+D' 2D' (c) D+D* 2D' D+D' 1000 1500 2000 2500 3000 D+D* D+D' 2D G In ensi y (a.u.) Raman shi (cm -1 ) Powde Sin e ed composi e (a) D 500 1000 1500 In ensi y (a.u.) Raman shi (cm -1 ) D G Figu e 4. ( a ) Raman spec a acqui ed on he composi e powde s a e high-ene gy plane a y ball milling and on he sin e ed composi e, inse : de ail o he Raman spec um acqui ed on he sin e ed composi e in he ange 150–1800 cm −1 ; ( b ) Decon olu ion o he i s -o de Raman spec um o he sin e ed composi e; ( c ) Decon olu ion o he second-o de Raman spec um o he sin e ed composi e (D +D*, 2D1, 2D2, 2D3, D +D’ and 2D’ bands). Ano he pa ame e ha can gi e in o ma ion abou de ec s in g aphene is he band wid h o D, G, D’ and 2D bands, as hei wid hs inc ease wi h a g owing numbe o de ec s [ 31 ]. Ma ins Fe ei a e al. [ 31 ] ha e epo ed ha he wid h o G and D’ peaks ha e a less p onounced dependence han he D and 2D bands. Acco ding o his assessmen , he band wid hs o he G and D’ peaks s ay in a iable in bo h he as-ex olia ed GNS and he sin e ed composi e (Table 2), while a lowe D band wid h is clea ly obse ed in he GNS a e sin e ing, which suppo s he dec ease o he numbe o de ec s men ioned abo e. Unexpec edly, he 2D band wid h s ays in a iable. Howe e , his pa ame e is no only dependen on he numbe o de ec s, bu also on o he ac o s such as doping o s ain [ 3 ]. I has been published ha he 2D band wid h o g aphene subjec ed o s ain su e s a b oadening and a shi in equency [ 3 , 44 , 45 ]. Table 2shows he posi ions o he D, G, D’ and 2D bands, e ealing a shi owa ds highe equencies o all o hem in he spec a o he GNS sin e ed composi e, in compa ison o he spec a o he as-ex olia ed GNS. This can be a ibu ed o esidual s esses in he GNS imposed by he cons aining ce amic ma ix [ 44 , 45 ]. Thus, he e ec o b oadening he 2D band as a consequence Ma e ials 2020,13, 2656 9 o 13 o he s esses would coun e ac he dec ease o he band wid h ela ed o he dec ease o de ec s in he GNs a e sin e ing. Table 2. Posi ions and band wid hs o he D, G, D’ and 2D bands ob ained o he as-syn hesized GNS and he GNS in he sin e ed composi e a e i ing he i s - and second-o de Raman spec a. Sample D G D’ 2D Posi ion (cm−1) Band Wid h (cm−1) Posi ion (cm−1) Band Wid h (cm−1) Posi ion (cm−1) Band Wid h (cm−1) Posi ion * (cm−1) Band Wid h * (cm−1) As-syn hesized GNS 1346.9 ±0.3 91.5 ±2.1 1585.34 ±1.02 52 ±1 1617.5 ±0.7 27.2 ±0.9 2687.6 ±0.4 103.96 ±1.6 Sin e ed 1 ol % GNS/3YTZP 1350.3 ±0.4 75.3 ±2.4 1592.1 ±1.3 53 ±2 1621.8 ±0.5 32.7 ±1.3 2690.9 ±1.1 105 ±3 * Values ob ained a e i ing he 2D band o a pseudo-Voig unc ion (no shown). Figu e 5shows he low magni ica ion SEM mic og aphs acqui ed on he polished c.s. su ace o he nanocomposi e using BSE. These images e lec he GNS dis ibu ion in he ce amic ma ix, as he 3YTZP ma ix and he GNS appea in he mic og aphs as ligh and da k phases, espec i ely. A homogeneous dis ibu ion o he GNS (ma ked wi h hin a ows in he igu e) h oughou he ce amic ma ix is obse ed, wi h sca ce la ge GNS agglome a es (ma ked wi h a hick a ow). In his c.s. image, mos o he obse ed nanoshee s p esen hei side iew, which indica es ha he ab plane o he g aphene laye s lies on a plane pe pendicula o he comp ession axis du ing sin e ing. This p e e en ial alignmen has been p e iously desc ibed o di e en ce amic composi es [ 19 , 24 , 25 , 41 ], including composi es p epa ed om powde s homogenized using plane a y ball milling in we condi ions [ 20 , 46 ]. This s uc u al aniso opy is a consequence o he wo-dimensional cha ac e o g aphene, and he uniaxial p essu e applied du ing he sin e ing p ocess. When inc easing he magni ica ion (inse in Figu e 5), e y hin GNS wi h la e al sizes o se e al mic ons can be obse ed h oughou he ma ix. This could co espond o in e connec ions o smalle GNS, as p e iously shown in he HRSEM images o he as-ex olia ed GNS (Figu e 1b). Ma e ials2020,13,xFORPEERREVIEW10o 14  Figu e5.BSE‐SEMmic og aphso  hepolishedc.s.su aceo  hesin e edcomposi e. TheHRSEMimageso  he ac u esu aceo  henanocomposi e,showninFigu e6,gi ean insigh in o hemo phologyo  heg aphenenanoshee sinco po a edin he3YTZPma ix.TheGNS (ma kedwi ha ows)appea aswa y,semi‐ anspa en  issueco e ing hece amicg ains,as p e iously epo edince amiccomposi eswi h ew‐laye g aphene[25,47].SomeGNScanbeseen omaside iew, e ealinga e ylow hickness,inacco dancewi h heHRSEMobse a ionso  he as‐syn hesizednanoshee s(Figu e1).The ac u esu acep esen samos lyin e g anula  ac u e mode,whichindica esas ongphysicalbondinga  hein e phasebe ween he3YTZPma ixand heGNS,al houghsomea easwi hin ag anula  ac u ecanalsobeobse ed.  Figu e6.HRSEMmic og aphso  he ac u esu aceo  hesin e edcomposi e.(a)SomeGNScanbe seenassemi‐ anspa en  issue;(b)someGNScanbeseen omaside iew. 3.3.Vicke sHa dnesso  heNanocomposi e TheVicke sha dnesso  henanocomposi e,e alua edoni.p.andc.s.su aces, e ealedno mechanicalaniso opy,assimila ha dness alueswe eob ained o bo hsu aces(Table3).This maybedue o hesmallla e alsizeo  heGNS.Also, he alueswe eiden ical o he epo edones o amonoli hic3YTZPce amicp epa edwi hsimila sin e ingcondi ions[41],and e ysimila  o he epo edones o acomposi ewi h1 ol%o g aphenenanoshee sob ainedbyex olia iono  comme cialg aphenenanopla ele sbymeanso high‐ene gyballmilling[23].These esul sindica e ha ce amic‐basedcomposi escon aining heelec ochemicallyex olia edGNSmayalsodisplay goodmechanicals eng hand ac u e oughness.Resea chwo k ode e mine hisisal eady unde way. Figu e 5. BSE-SEM mic og aphs o he polished c.s. su ace o he sin e ed composi e. The HRSEM images o he ac u e su ace o he nanocomposi e, shown in Figu e 6, gi e an insigh in o he mo phology o he g aphene nanoshee s inco po a ed in he 3YTZP ma ix. The GNS (ma ked wi h a ows) appea as wa y, semi- anspa en issue co e ing he ce amic g ains, as p e iously epo ed in ce amic composi es wi h ew-laye g aphene [ 25 , 47 ]. Some GNS can be seen om a side iew, e ealing a e y low hickness, in acco dance wi h he HRSEM obse a ions o he as-syn hesized nanoshee s (Figu e 1). The ac u e su ace p esen s a mos ly in e g anula ac u e mode, which indica es a s ong physical bonding a he in e phase be ween he 3YTZP ma ix and he GNS, al hough some a eas wi h in ag anula ac u e can also be obse ed.