Structural and Vibrational Properties of Corundum-type In2O3 Nanocrystals under Compression

1 S uc u al and Vib a ional P ope ies o Co undum- ype In2O3 Nanoc ys als unde Comp ession J.A. Sans,1,* R. Vilaplana,2 D. E andonea,3 V.P. Cuenca-Go o ,1 B. Ga cía-Domene,3 C. Popescu,4 F. J. Manjón,1 A. Singhal,5 S. N. Acha y,5 D. Ma inez-Ga cia,3 J. Pellice - Po es,3 P. Rod íguez-He nández,6 and A. Muñoz 6 1 Ins i u o de Diseño pa a la Fab icación y P oducción Au oma izada, MALTA Consolide Team-Uni e si a Poli ècnica de València, 46022 València, Spain 2 Cen o de Tecnologías Físicas: Acús ica, Ma e iales y As o ísica, MALTA Consolide Team, Uni e si a Poli ècnica de València, 46022 València, Spain 3 Depa amen o de Física Aplicada-ICMUV, MALTA Consolide Team, Uni e sidad de Valencia, Edi icio de In es igación, C/D . Moline 50, Bu jasso , 46100 Valencia, Spain 4 ALBA-CELLS, Ce danyola, 08290 Ba celona, Spain 5 Chemis y Di ision, Bhabha A omic Resea ch Cen e, T ombay, Mumbai 400085, India 6 Depa amen o de Física, Ins i u o de Ma e iales y Nano ecnología, MALTA Consolide Team, Uni e sidad de La Laguna, 38205 Tene i e, Spain E-mail: [email p o ec ed] ABSTRACT This wo k epo s he s uc u al and ib a ional p ope ies o nanoc ys als o co undum- ype In2O3 ( h-In2O3) a high p essu es by using angle-dispe si e x- ay di ac ion and Raman sca e ing measu emen s up o 30 GPa. The equa ion o s a e and he p essu e dependence o he Raman-ac i e modes o he co undum phase in nanoc ys als a e in good ag eemen wi h p e ious s udies on bulk ma e ial and compa e nicely wi h heo e ical simula ions on bulk h-In2O3. Nanoc ys alline h-In2O3 showed s abili y unde comp ession a leas up o 20 GPa, unlike bulk h-In2O3 which g adually ans o ms o he o ho hombic Pbca (Rh2O3-III- ype) s uc u e abo e 12-14 GPa. The di e en s abili y ange ound in nanoc ys alline and bulk In2O3 is discussed. KEYWORDS: indium oxide, nanoc ys als, co undum, X- ay di ac ion, Raman spec oscopy, high-p essu e, ab ini io calcula ions 1. In oduc ion Indium oxide (In2O3) is a sesquioxide whose s able phase a oom condi ions is he cubic bixbyi e- ype s uc u e1 (space g oup (SG) Ia-3, N. 206, Z=16). This phase has been widely s udied o op oelec onic applica ions due o i s special p ope ies as a anspa en conduc ing oxide (TCO).2,3 The widesp ead use o cubic In 2O3 (c-In2O3) in indus ial p ocesses co e s he 2 ab ica ion o window laye s in sola cells,3-5 ligh -emi ing diodes,6,7 elec och omic windows,8 liquid-c ys al displays,9,10 and gas senso s. 11,12 Howe e , he sca ci y and high cos o ob ain indium me al has led o he s udy o new sys ems, like Sn-doped In2O3 (ITO) and In2−2xZnxSnxO3 (x ≤ 0.4, also named ZITO o IZTO), in o de o cu he p ice o i s p oduc ion p ocess.13−15 Rhombohed al co undum- ype (SG R-3c, N. 167, Z= 6) In 2O3 is also known o be a me as able phase a oom condi ions ha can be ob ained a e high p essu e (HP)-high empe a u e (HT) ea men , bu also a oom p essu e.16-40 Mode n calcula ions o pu e and doped hombohed al In2O3 ( h-In2O3), sugges ha his phase could be e en be e TCO han c-In2O3; hus opening a new way o sea ch o imp o ed TCOs.41-44 Gi en he abo e esul , i is clea ha he s udy o he HP phases (pe haps me as able a ambien condi ions) o a echnological impo an compound, like In 2O3, is c ucial o he ad ancemen o science and echnology.45-47 In his espec , h ee addi ional o ho hombic phases o In2O3 ha e been heo e ically p edic ed and indeed ob ained by applica ion o HP: Rh2O3-III ype (SG Pbca, N. 61, Z= 8),36,37 Rh2O3-II ype (SG Pbcn, N. 60, Z= 4),32, 48-51 and -Gd2S3- ype (SG Pnma, N. 62, Z= 4).52 Among hem only he Pbcn phase has been claimed o be me as able a ambien condi ions,49-51 despi e he Pbca phase is a phase epo ed a lowe p essu es han he Pbcn phase.36,37 Wo king wi h nanoc ys als opens he doo o enhanced p ope ies o ma e ials;53,54 and adds he possibili y o ob aining me as able HP c ys alline and amo phous phases a oom condi ions wi h di e en p ope ies om he o iginal ma e ial.47,55-57 I is well known ha mos nanoc ys als unde go a p essu e-induced phase ansi ion a la ge p essu es han in he bulk and ha many nanoc ys als unde go a p essu e-induced amo phiza ion;55 howe e , many ques ions emain open ega ding he beha iou o nanoc ys als a HP in compa ison wi h bulk ma e ials. In 3 pa icula , he di e en he modynamic s abili y o c ys alline phases in nanoc ys als as compa ed o bulk ma e ial,55,56 and whe he he comp essibili y o nanoc ys als is di e en o ha o bulk ma e ial o i he di e en comp essibili y comes om a di e en deg ee o hyd os a ici y a ec ing mic o and nanoc ys al powde s. E en i se e al wo ks ha e been de o ed o he s udy o In2O3 nanoc ys als a HP, mos o hem ha e ocused on nanoc ys als o cubic bixbyi e- ype In2O3,58-60 and only a small pa ha e been de o ed o s udy nanoc ys als o hombohed al co undum- ype In2O3.49,50,59 In ac , a di e en s abili y ange o he homobohed al phase unde comp ession has been obse ed depending on he sample size. Gu lo e al., who s udied nanoc ys als o h-In2O3, sugges ed ha his compound is s able a oom empe a u e be ween oom p essu e and 30 GPa;49 howe e , wo ecen s udies epo ed ha bulk h-In2O3 unde goes a ans o ma ion abo e 12-14 GPa in good ag eemen wi h heo e ical simula ions.36,37 The appa en lack o phase ansi ion in nanoc ys als up o 30 GPa sugges s he exis ence o la ge kine ic ba ie s o explain hei ex ended s uc u al s abili y. In his wo k we epo a HP s udy o he s uc u al and ib a ional p ope ies o nanoc ys als o co undum- ype In2O3 by means o angle-dispe si e powde x- ay di ac ion (XRD) and Raman sca e ing (RS) measu emen s up o 30 GPa. Bo h he equa ion o s a e and he p essu e dependence o he Raman-ac i e modes o he co undum phase in nanoc ys als a e epo ed, showing a nice ag eemen wi h p e ious s udies on h-In2O3 nanoc ys als.49 These esul s ha e been compa ed wi h expe imen al and heo e ical s uc u al and la ice dynamics esul s on bulk h-In2O3 o e ing an explana ion o he p e iously appa en con adic ing esul s obse ed be ween bulk and nanoc ys alline h-In2O3. 4 2. Me hods 2.1. Expe imen al de ails Rh-In2O3 nanopa icles we e syn hesized by he mal dehyd a ion o InOOH nanopa icles p e iously p epa ed om a sol o he mal eac ion be ween indium ni a e and e ame hylammonium hyd oxide.61 XRD measu emen s con i m ha nanoc ys alline powde s a e pu e and ha e co undum- ype s uc u e wi h an hexagonal uni cell wi h la ice pa ame e s a=b= 5.485 Å and c= 14.530 Å, which a e in good ag eemen wi h e e ence JCPDS ca d 220336 (a=b= 5.487 Å and c= 14.510 Å). On he o he hand, ansmission elec on mic oscopy (TEM) con i med bo h he c ys alline s uc u e and pu i y and de e mined ha nanoc ys als ha e a ice-g ain ype mo phology wi h an a e age leng h (wid h) o 20 (13) nm and a uni o m dis ibu ion be ween 10 (6) and 30 (20) nm.61 Room- empe a u e expe imen s in h-In2O3 nanoc ys als we e conduc ed up o 30 GPa in a memb ane- ype diamond an il cell. In HP-XRD and HP-RS expe imen s, powde sample was loaded inside a 150 m diame e hole d illed in an inconel gaske oge he wi h a mix u e o me hanol-e hanol-wa e (MEW) in a 16:3:1 p opo ion as a quasi-hyd os a ic p essu e- ansmi ing medium (PTM) as in a p e ious wo k,37 in o de o compa e esul s o bulk and nanoc ys alline h-In2O3 unde he same condi ions. Addi ionally, a second XRD expe imen wi h A as PTM was done in o de o p o e i nanopowde s could be a ec ed by non-hyd os a ic e ec s using MEW and o compa e wi h p e ious esul s desc ibed in he li e a u e.37 Fo p essu e calib a ion in angle-dispe si e powde XRD and RS measu emen s we in oduced inside he p essu e ca i y Cu powde 62 and uby,63 espec i ely. In he XRD expe imen s we collec ed also wo pa e ns, one in he egion whe e he Cu peaks we e s ong and he o he whe e he e is no Cu signal. The i s pa e n was used o de e mine p essu e and he second one o analyse he c ys al s uc u e o In2O3. 5 Angle-dispe si e powde XRD measu emen s a di e en p essu es we e pe o med in he MSPD beamline64 a ALBA synch o on acili y. This beamline is equipped wi h Ki kpa ick-Baez mi o s o ocus he monoch oma ic beam and a SX165 CCD de ec o wi h a diame e o 165 mm. We used a wa eleng h o 0.4246 Å and he sample-de ec o dis ance du ing he expe imen was se o 240 mm. The 2-D di ac ion images we e in eg a ed wi h FIT2D so wa e.65 La ice pa ame e s o XRD pa e ns we e ob ained wi h Rie eld e inemen s pe o med using POWDERCELL66 and GSAS67 p og am packages. On he o he hand, RS measu emen s a oom empe a u e and di e en p essu es we e exci ed using he 632.8 nm HeNe lase (wi h a powe below10 mW) and collec ed in backsca e ing geome y wi h a Ho iba Jobin Y on LabRam HR UV spec ome e equipped wi h a he moelec ically cooled mul ichannel CCD de ec o ( esolu ion below 2 cm-1). 2.2.Theo e ical Calcula ions To al-ene gy ab ini io calcula ions we e pe o med o bulk h-In2O3 wi hin he densi y unc ional heo y (DFT)68 using he Vienna Ab ini io Simula ion Package (VASP)69 as desc ibed in Re . 37 o bulk h-In2O3. In pa icula , we ha e used he p ojec o -augmen ed wa e (PAW)70 scheme implemen ed in his package and he gene alized g adien app oxima ion (GGA) was used o he desc ip ion o he exchange-co ela ion ene gy wi h he PBEsol p esc ip ion.71 We ha e also pe o med la ice dynamics calcula ions o he phonon modes in bulk h- In2O3 a he cen e o he BZ ( poin ) using he di ec o ce cons an app oach (o supe cell me hod)72 al eady desc ibed in Re . 37. Ou heo e ical esul s p o ide bo h he equencies o he no mal modes and hei pola iza ion ec o s and enable us o assign he Raman-ac i e modes obse ed in nanoc ys alline h-In2O3 as p e iously done o bulk h-In2O3.37 6 3. Resul s 3.1. XRD measu emen s Figu e 1a shows a selec ion o he expe imen al angle-dispe si e powde XRD pa e ns o h-In2O3 a oom empe a u e a di e en p essu es up o 21 GPa ob ained in he i s expe imen (using MEW mix u e as PTM). Figu e 1b shows simila esul s up o 29.8 GPa ob ained in he second expe imen (using A as PTM). All he XRD pa e ns can be indexed wi h he co undum- ype s uc u e. Unde comp ession some o he peaks shi as e o highe angles han o he s due o he aniso opic comp essibili y o In2O3 which will be discussed in de ail la e . This phenomenon is illus a ed in Figs. 1a and 1b by he (104) and (110) B agg peaks which g adually me ge unde comp ession because he in e plana dis ance associa ed o he (104) peak dec eases as e unde comp ession han ha co esponding o he (110) e lec ion. In he second expe imen , in addi ion o he B agg peaks o he sample, B agg peaks o A a e also de ec ed. These peaks can be easily iden i ied because, due o he la ge comp essibili y o A , hey shi as e o highe angles unde comp ession han he peaks co esponding o In2O3. The A peaks we e used o con i m he p essu e de e mined om Cu using he equa ion o s a e o A .73 The p essu e de e mined om A ag ees wi hin 0.1 GPa wi h he p essu e de e mined om Cu. The esul s o bo h XRD expe imen s indica e ha he phase ansi ion o he Pbca- ype phase obse ed in bulk h-In2O3 abo e 12-14 GPa,36,37 is no obse ed in nanoc ys als e en a 29.8 GPa. We would like o commen he e ha beyond 20 GPa all he peaks assigned o co undum- ype In2O3 can be also explained wi h he Pbca- ype s uc u e. Howe e , his s uc u e has a peak a low angles, he (002) peak expec ed o be loca ed a ound 3.2º, which is no p esen in he co undum- ype s uc u e. In ou expe imen s, we did no obse e his peak, which suppo s he s abili y o he co undum- ype s uc u e up o 7 29.8 GPa. This esul is in ag eemen wi h he la ge s abili y o he co undum phase measu ed by Gu lo e al. in nanoc ys alline h-In2O3 samples wi h pa icle size be ween 50 and 100 nm.49 XRD peaks in ou i s expe imen show sligh b oadening wi h inc easing p essu e abo e 10 GPa which could be due o a sligh loss o quasi-hyd os a ic condi ions o he PTM. The same b oadening is obse ed in he second expe imen bu a ound 20 GPa. This is a consequence o he be e quasi- hyd os a ic condi ions gene a ed by A han by MEW abo e 10 GPa.74 In his ega d, i is expec ed ha small non-hyd os a ic s esses do no in luence he s uc u al s abili y o ela i ely uncomp essible compounds like sesquioxides.75 In his wo k, we ha e ex ac ed he e olu ion o he s uc u al pa ame e s o nanoc ys alline h-In2O3 unde comp ession by Rie eld e inemen . In Figu e 1, one can see he expe imen al di ac ion pa e n (black symbols), he Rie eld e inemen pe o med (black line) and he esiduals ( ed lines) showing a good i o he expe imen al da a. Figu e 2 ep esen s he expe imen al p essu e dependence o he hexagonal uni -cell olume, la ice pa ame e s a and c and he c/a a io in nanoc ys alline h-In2O3. The expe imen al da a o he uni -cell olume up o 29.8 GPa can be i ed wi h a hi d-o de Bi ch-Mu naghan (BM) EOS,76,77 which yields V0= 376.7(4) A3, B0= 169(6) GPa and B0’= 6.2(9). These alues a e in good ag eemen wi h heo e ical da a o bulk ma e ial i ed up o 30 GPa (V0= 383.3 A3, B0= 169 GPa and B0’= 3.3) and wi h p e ious expe imen al (B0= 176-180 GPa) and heo e ical es ima ions in bulk ma e ial.37 No e ha he alue o he bulk modulus o h-In2O3 nanoc ys als is sligh ly smalle han ha in bulk ma e ial (see Table I). In ela ion o his, i mus be no ed ha a dec ease o he bulk modulus in nanoc ys als wi h espec o bulk ma e ial has been obse ed in a numbe o oxides, like TiO2,78,79 Z O2,80,81 SnO2,82 MgO,83 ZnO,84 and Al2O3.85 8 A de ia ion o he comp essibili y o nanoc ys als abo e ce ain p essu e has been ound in o he wo ks. In pa icula , nanoc ys als o ana ase TiO2 p essu ized wi h a 4:1 me hanol-e hanol mix u e we e ound o unde go de ia ions o he comp essibili y o he a axis and uni -cell olume abo e 10-12 GPa which we e a ibu ed o he appea ance o an in e media e local dis o ion (~ 2 Å) wi h TiO2-II s uc u e.86 On he o he hand, a signi ican ly lowe bulk modulus (148±5 GPa) compa ed o heo e ical calcula ions (169.4 GPa) has been ecen ly obse ed in c-In2O3 nanoc ys als wi h a high de ec densi y unde comp ession wi h a 4:1 me hanol-e hanol mix u e as PTM.60 In ha wo k, au ho s claimed ha he di e en bulk modulus o wo nanoc ys alline samples wi h simila sizes and mo phologies we e due o hei di e en de ec densi ies. Ano he possibili y is ha he change in comp essibili y obse ed abo e 8 GPa in In2O3 nanoc ys als could be due o non-hyd os a ic condi ions as i was easoned o nanoc ys alline TiO2 ana ase.78 No e ha nanoc ys alline powde is mo e p one o non-hyd os a ic condi ions han bulk powde because he su ace a ea o nanoc ys alline g ains end o be mo e su ounded by o he nanoc ys alline g ains han by he molecules o he PTM. On he o he hand, he su ace a ea o mic oc ys alline g ains end o be mo e su ounded by he molecules o he PTM han by o he g ains. In any case, i was demons a ed o nanoc ys alline TiO2 ana ase ha he EOS ob ained p io o obse a ion o non-hyd os a ic condi ions is in good ag eemen wi h he EOS ob ained unde uly hyd os a ic condi ions along he whole ange o he expe imen s.78 Since measu emen s in nanoc ys alline h- In2O3 using MEW o A show simila esul s (see Fig. 2), we a e con iden o he bulk modulus ob ained o nanoc ys als wi h an a e age g ain size a ound 20 nm up o 30 GPa. I mus be s essed ha he bulk modulus we ha e ob ained o h-In2O3 nanoc ys als in he p esen s udy is much smalle han ha epo ed (305 GPa) in a p e ious wo k.58 In ac , Re . 58 also epo s an o e es ima ion o he bulk modulus in h-In2O3 as was also con i med in ou p e ious wo k.37 The 9 main eason o he o e es ima ion o he bulk modulus in Re . 58 is he lack o s uc u al da a o he co undum- ype phase a low p essu es and he inhe en unce ain y caused by he ex apola ion o he bulk modulus om da a abo e 20 GPa. On he o he hand, bo h a and c la ice pa ame e s show a a he simila p essu e dependence in bo h bulk ma e ial and nanoc ys als, also obse ed in he c/a a io (inse o igu e 2b). The la ice pa ame e s o h-In2O3 nanoc ys als show an almos linea a ia ion wi h p essu e. Bo h a and c pa ame e s ha e been i ed o a modi ied Mu naghan’s equa ion wi h ee pa ame e s a0, B0 and B0’. 󰇡1 󰆓 󰇢󰇧   󰆓󰇨 , Eq. (1) The esul s o hese i s a e shown in Table II. The axial comp essibili ies o he a- and c-axis de ined as P x x x  1  (whe e x = a, c) can be ob ained as 0 3 1 B x  wi h he B0 alues ob ained wi h he Mu naghan EOS i o he la ice pa ame e s. The expe imen al comp essibili y o he a (c) axis is 1.4 (3.0) ·10-3 GPa-1 This esul indica es ha he c axis is mo e han wo imes mo e comp essible han he a axis as i occu s in bulk h-In2O3.37 Consequen ly, we can conclude ha he majo con ibu ion o he comp essibili y o nanoc ys alline h-In2O3 comes om he la ge comp essibili y o he c axis han ha o he a axis. These beha iou s a e in ag eemen wi h expe imen s and heo e ical calcula ions al eady published o bulk h-In2O337 and heo e ical calcula ions (Table II). Simila ly, he c/a a io in bulk and nanoc ys alline h-In2O3 shows he same endency in good ag eemen wi h ou heo e ical calcula ions; howe e , his beha iou is di e en o ha epo ed in co undum- ype Al2O3, V2O3, C 2O3, and Fe2O3,87 as al eady discussed in ou p e ious wo k ega ding bulk h-In2O3.37 16 1b Figu e 1. Selec ed X- ay di ac ion pa e ns o nanoc ys alline h-In2O3 a se e al p essu es using MEW (a) and A (b) as PTM. Di ac ion pa e ns ha e been shi ed e ically o cla i y. Di e en di ac ion peaks a e assigned in he g aph o h-In2O3 (R-3c), A and Cu phases. Re inemen s and esiduals o he i o hese phases a e also shown. 17 Figu e 2. P essu e dependence o he uni -cell pa ame e s (a) and olume (b) in nanoc ys alline h-In 2 O 3 o ou i s expe imen (close symbols) and he second expe imen (open symbols). The inse shows he p essu e dependence o he c/a a io in nanoc ys alline h-In 2 O 3 . Red dashed lines co espond o heo e ical da a o bulk h-In 2 O 3 . 18 Figu e 3. Selec ed RS spec a o nanoc ys alline h-In2O3 a di e en p essu es on ups oke up o 29.3 GPa. In he RS spec um a 0.2 GPa, i s -o de Raman modes o h-In2O3 a e indica ed by a ows, while second-o de Raman modes a e deno ed wi h as e isks. Abo e 20 GPa, a ows in he RS spec a indica e he new peaks assigned o he Pbca phase. The op RS spec um a 2.3 GPa shows he e e sibili y o he sample o he co undum phase on downs oke. 19 Figu e 4. P essu e dependence o he Raman-ac i e mode equencies in nanoc ys alline h-In2O3 ( iole ci cles) and Pbca- ype In2O3 (o ange squa es). Full (emp y) symbols co espond o he ups oke (downs oke) p ocess. Solid lines co espond o ab ini io simula ed Raman-ac i e modes o bulk h-In2O3. The symme y o he Raman-ac i e modes o h-In2O3 is indica ed. 20 TABLES Table I. Compa ison o heo e ical and expe imen al ze o p essu e uni -cell olume pe o mula uni , bulk modulus, and i s p essu e de i a i e o bulk and nanoc ys alline h-In2O3. Phase V 0 (Å3) B0 (GPa) B’0 Me hod nano R-3c 62.78(1) 169(6) 6.2(9) Exp. (XRD)a R-3c 61.49 305.5 2.9 Exp. (XRD) b bulk R-3c 62.86(4) 180(7) 3.2(1.2) Exp. (XRD)c R-3c 63.88 167 3.3 Theo. (GGA- PBEsol)d a This wo k b Re . 58 c Re . 37 d Da a up o 30 GPa. 21 Table II. La ice pa ame e s and hei bulk modulus and p essu e de i a i e o bulk modulus a oom p essu e in nanoc ys alline h-In2O3 ( op) as compa ed o expe imen al and heo e ical pa ame e s in bulk Exp. h-In2O3 (bo om) a0 (Å) B0a (GPa) Ba’ c0 (Å) B0c (GPa) Bc’ Me hod 5.4831(8) 233(16) 11.8 14.461(8) 109(3) 0.48 Ou Exp. (XRD) 5.479(2) 220(30) 11.8 14.511(5) 121(7) 0.48 Exp. (XRD) 5.520(1) 216(3) 11.8(4) 14.552(1) 106.0(9) 0.48(11) Theo. (GGA- PBEsol) 22 Table III. Room-p essu e expe imen al equencies, p essu e coe icien s and G üneisen pa ame e s o he Raman ac i e modes o bulk and nanoc ys alline h-In2O3. Bulk h-In2O3 Nano h-In2O3 Abini iocalcula ions Expe imen albExpe imen al Mode (Sym)  cm-1  a cm-1    cm-1  c A1 g 156(1) 0.65 (3) -0.012 (2) 0.66 162.3 (2) 0.85 (4) -0.015 (1) 0.93 163.2(2) 0.590(14) 0.61 E g 169(1) 0.73 (3) -0.010 (2) 0.68 177.1 (2) 1.01 (6) -0.022 (3) 1.01 181.3(5) 0.54(4) 0.50 E g 214(1) 1.54 (3) -0.023 (2) 1.14 218.1 (3) 1.85 (8) -0.039 (5) 1.50 223.9(5) 1.30(3) 0.97 E g 265(1) 1.11 (6) -0.005 (5) 0.66 270.7 (4) 1.33 (13) -0.011 (7) 0.87 270(1) 1.49(11) 0.93 E g 373(2) 4.91 (5) -0.040 (4) 2.08 383.8 (6) 4.69 (16) -0.022 (8) 2.16 388.3(9) 4.61(6) 2.0 A1 g 486(2) 4.46 (6) -0.033 (4) 1.45 501.9 (9) 3.92 (25) 0.005 (14) 1.38 502.5(6) 4.75(5) 1.6 E g 569(2) 6.14 (5) -0.059 (4) 1.70 590.3 (6) 5.95 (18) -0.058 (12) 1.78 599(1) 5.42(11) 1.53 a Theo e ical B0= 158 GPa used o calcula ing he G üneisen pa ame e . b F om e . 37 (expe imen al B0= 177 GPa used o calcula ing he G üneisen pa ame e ). c Expe imen al B0= 169 GPa used o calcula ing he G üneisen pa ame e . P           GPa cm 1 2 2 P           2 1 GPa cm P            GPa cm 1 2 2 P           2 1 GPa cm P            GPa cm 1 23 Au ho Con ibu ions The manusc ip was w i en h ough con ibu ions o all au ho s. All au ho s ha e gi en app o al o he inal e sion o he manusc ip . Acknowledgmen s This wo k is suppo ed by he Spanish MICINN p ojec s MAT2016-75586-C4-1/2/4-P and MAT2015-71070-REDC. A.M. and P.R-H acknowledge compu ing ime p o ided by Red Española de Supe compu ación (RES) and MALTA-Clus e . J.A.S. acknowledges inancial suppo h ough he Ramon y Cajal ellowship. Re e ences 1 Ma ezio M 1966 Re inemen o he C ys al S uc u e o In2O3 a wo Wa eleng hs Ac a C ys allog . 20 723-728. 24 2 Mizoguchi H and Woodwa d P M 2004 Elec onic S uc u e S udies o Main G oup Oxides Possessing Edge-Sha ing Oc ahed a: Implica ions o he Design o T anspa en Conduc ing Oxides Chemis y o Ma e ials 16 5233-5248. 3 B eeze A J e al 2001 Cha ge anspo in TiO2/MEH-PPV polyme pho o ol aics Physical Re iew B 64 125205. 4 Taha R B H e al 1998 Tin doped indium oxide hin ilms: Elec ical p ope ies J. Appl. Phys. 83 2631-2645. 5 Kaspa T C e al 2011 ZnO/Sn:In2O3 and ZnO/ CdTe Band O se s o Ex emely Thin Abso be Pho o ol aics Appl. Phys. Le . 99 263504. 6 Tang C W and Vanslyke S A 1987 O ganic elec oluminescen diodes Appl. Phys. Le . 51 913 7 Tang L-M e al 2010 Dono -dono binding in In2O3: Enginee ing shallow dono le els J. Appl. Phys. 107 083704 8 S eele B C H and Golden S J 1991 Va iable ansmission elec och omic windows u ilizing indoped indium oxide coun e elec odes Appl. Phys. Le . 59 2357 9 Lee B H e al 1997 E ec o p ocess pa ame e s on he cha ac e is ics o indium in oxide hin ilm o la panel display applica ion Thin Solid Films 302 25-30 10 Hsu S F e al 2005 Highly e icien op-emi ing whi e o ganic elec oluminescen de ices Appl. Phys. Le . 86 253508 11 Himme lich M e al 2012 Su ace p ope ies o s oichiome ic and de ec - ich indium oxide ilms g own by MOCVD J. Appl. Phys. 111 093704 12 X. Lai e al 2010 O de ed A ays o Bead-Chain-like In2O3 Nano ods and Thei Enhanced Sensing Pe o mance o Fo maldehyde Chemis y o Ma e ials 22 3033-3042 25 13 Rau I A 1993 Low Resis i i y and High Mobili y Tin-Doped Indium Oxide Films Ma e . Le . 18 123−127 14 Palme G B e al 1997 Conduc i i y and T anspa ency o ZnO/SnO2-Cosubs i u ed In2O3 Chem. Ma e . 9 3121−3126. 15 Hoel C A e al 2010 High-P essu e Syn hesis and Local S uc u e o Co undum-Type In2−2xZnxSnxO3 (x ≤ 0.7) J. Am. Chem. Soc. 132 16479−16487. 16 Shannon R D 1966 New High P essu e Phases Ha ing The Co undum S uc u e Solid S a e Commun. 4 629-630 17 No dlund Ch is ensen A e al 1967 Hyd o he mal In es iga ion o he Sys ems In2O3·H2O·Na2O and In2O3·D2O·Na2O. The C ys al S uc u e o Rhombohed al In2O3 and o In(OH)3 Ac . Chem. Scan. 21 1046-1056 18 P ewi C T e al 1969 The C Ra e Ea h Oxide-Co undum T ansi ion and C ys al Chemis y o Oxides Ha ing he Co undum S uc u e Ino g. Chem. 8 1985-1993 19 A ou T e al 1990 Shock-Induced Phase T ansi ion o M203 (M = SC, Y, Sm, Gd, and In)- Type Compounds J. Solid S a e Chem. 89 378-384 20 Gu lo A e al 2003 Polyc ys alline Well-Shaped Blocks o Indium Oxide Ob ained by he Sol-Gel Me hod and hei Gas-Sensing P ope ies Chemis y o Ma e ials 15 4377-4383 21 Gu lo A e al 2003 Co undum- ype indium (III) oxide: o ma ion unde ambien condi ions in Fe2O3–In2O3 sys em Ino g. Chem. Comm. 6 569-572 22 Yu D B e al 2003 Me as able Hexagonal In2O3 Nano ibe s Templa ed om InOOH Nano ibe s unde Ambien P essu e Ad . Func . Ma e . 13 497-501 23 Seo W S e al 2003 P epa a ion and Op ical P ope ies o Highly C ys alline, Colloidal, and Size-Con olled Indium Oxide Nanopa icles Ad . Ma e . 15 795-797