TY - JOUR
T1 - Enhancement of Electrical Conduction and Phonon Scattering in Ga 2 O 3 (ZnO) 9 -In 2 O 3 (ZnO) 9 Compounds by Modification of Interfaces at the Nanoscale
AU - Alvarez-Ruiz, Diana T.
AU - Azough, Feridoon
AU - Hernandez-Maldonado, David
AU - Kepaptsoglou, Demie M.
AU - Ramasse, Quentin M.
AU - Svec, Peter
AU - Svec, Peter
AU - Freer, Robert
N1 - Funding Information:
The authors are grateful to the EPSRC for the provision of funding for this work (EP/H043462, EP/ I036230/1, EP/L014068/1, EP/L017695/1 are acknowledged by RF). SuperSTEM is the EPSRC National Facility for Advanced Electron Microscopy, supported by EPSRC. All research data supporting this publication are directly available within the publication.
Publisher Copyright:
© 2018, The Minerals, Metals & Materials Society.
PY - 2019/4/15
Y1 - 2019/4/15
N2 - The Ga 2 O 3 (ZnO) 9 and In 2 O 3 (ZnO) 9 homologous phases have attracted attention as thermoelectric (TE) oxides due to their layered structures. Ga 2 O 3 (ZnO) 9 exhibits low thermal conductivity, while In 2 O 3 (ZnO) 9 possesses higher electrical conductivity. The TE properties of the solid solution of Ga 2 O 3 (ZnO) 9 -In 2 O 3 (ZnO) 9 were explored and correlated with changes in the crystal structure. High-quality (1−x)Ga 2 O 3 (ZnO) 9 -(ZnO) 9 (x = 0.0 to 1.0) ceramics were prepared by the solid-state route using B 2 O 3 and Nd 2 O 3 as additives. The crystal structures were analysed by x-ray diffraction, high-resolution transmission electron microscopy and atomic resolution scanning transmission electron microscopy–high-angle annular dark field imaging–energy dispersive x-ray spectroscopy (STEM–HAADF–EDS) techniques. A layered superstructure with compositional modulations was observed in all samples in the (1−x)Ga 2 O 3 (ZnO) 9 -xIn 2 O 3 (ZnO) 9 system. All the ceramics exhibited nanoscale structural features identified as Ga- and In-rich inversion boundaries (IBs). Substitution of 20 mol.% In (x = 0.2) in the Ga 2 O 3 (ZnO) 9 compounds generated basal and pyramidal indium IBs typically found in the In 2 O 3 (ZnO) m system. The (Ga 0.8 In 0.2 ) 2 O 3 (ZnO) 9 compound does not exhibit the structural features of the Cmcm Ga 2 O 3 (ZnO) 9 compound, which is formed by a stacking of Ga-rich IBs along the pyramidal plane of the wurtzite ZnO, but features that resemble the crystal structure exhibited by the R3 ¯ m In 2 O 3 (ZnO) m with basal and pyramidal indium IBs. The structural changes led to improved TE performance. For example, (Ga 0.8 In 0.2 ) 2 O 3 (ZnO) 9 showed a low thermal conductivity of 2 W/m K and a high power factor of 150 μW/m K 2 giving a figure of merit (ZT) of 0.07 at 900 K. This is the highest ZT for Ga 2 O 3 (ZnO) 9 -based homologous compounds and is comparable with the highest ZT reported for In 2 O 3 (ZnO) 9 homologous compounds.
AB - The Ga 2 O 3 (ZnO) 9 and In 2 O 3 (ZnO) 9 homologous phases have attracted attention as thermoelectric (TE) oxides due to their layered structures. Ga 2 O 3 (ZnO) 9 exhibits low thermal conductivity, while In 2 O 3 (ZnO) 9 possesses higher electrical conductivity. The TE properties of the solid solution of Ga 2 O 3 (ZnO) 9 -In 2 O 3 (ZnO) 9 were explored and correlated with changes in the crystal structure. High-quality (1−x)Ga 2 O 3 (ZnO) 9 -(ZnO) 9 (x = 0.0 to 1.0) ceramics were prepared by the solid-state route using B 2 O 3 and Nd 2 O 3 as additives. The crystal structures were analysed by x-ray diffraction, high-resolution transmission electron microscopy and atomic resolution scanning transmission electron microscopy–high-angle annular dark field imaging–energy dispersive x-ray spectroscopy (STEM–HAADF–EDS) techniques. A layered superstructure with compositional modulations was observed in all samples in the (1−x)Ga 2 O 3 (ZnO) 9 -xIn 2 O 3 (ZnO) 9 system. All the ceramics exhibited nanoscale structural features identified as Ga- and In-rich inversion boundaries (IBs). Substitution of 20 mol.% In (x = 0.2) in the Ga 2 O 3 (ZnO) 9 compounds generated basal and pyramidal indium IBs typically found in the In 2 O 3 (ZnO) m system. The (Ga 0.8 In 0.2 ) 2 O 3 (ZnO) 9 compound does not exhibit the structural features of the Cmcm Ga 2 O 3 (ZnO) 9 compound, which is formed by a stacking of Ga-rich IBs along the pyramidal plane of the wurtzite ZnO, but features that resemble the crystal structure exhibited by the R3 ¯ m In 2 O 3 (ZnO) m with basal and pyramidal indium IBs. The structural changes led to improved TE performance. For example, (Ga 0.8 In 0.2 ) 2 O 3 (ZnO) 9 showed a low thermal conductivity of 2 W/m K and a high power factor of 150 μW/m K 2 giving a figure of merit (ZT) of 0.07 at 900 K. This is the highest ZT for Ga 2 O 3 (ZnO) 9 -based homologous compounds and is comparable with the highest ZT reported for In 2 O 3 (ZnO) 9 homologous compounds.
KW - homologous compounds
KW - interfaces
KW - inversion boundaries
KW - thermoelectric
KW - twin boundaries
KW - ZnO
UR - http://www.scopus.com/inward/record.url?scp=85058857787&partnerID=8YFLogxK
U2 - 10.1007/s11664-018-06878-w
DO - 10.1007/s11664-018-06878-w
M3 - Article
AN - SCOPUS:85058857787
SN - 0361-5235
VL - 48
SP - 1818
EP - 1826
JO - Journal of Electronic Materials
JF - Journal of Electronic Materials
IS - 4
ER -