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

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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.