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

Diana T. Alvarez-Ruiz, Feridoon Azough, David Hernandez-Maldonado, Demie M. Kepaptsoglou, Quentin M. Ramasse, Peter Svec, Peter Svec, Robert Freer

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)1818-1826
Number of pages9
JournalJournal of Electronic Materials
Issue number4
Publication statusPublished - 15 Apr 2019


  • homologous compounds
  • interfaces
  • inversion boundaries
  • thermoelectric
  • twin boundaries
  • ZnO


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