Phase Transformation of Metastable Cu2ZnGeO4 with a Wurtz-Kesterite Structure at Elevated Temperatures

Masao Kita; Issei Suzuki; Noriyuki Wada; Takahisa Omata

doi:10.1021/acs.inorgchem.2c00480

Phase Transformation of Metastable Cu₂ZnGeO₄ with a Wurtz-Kesterite Structure at Elevated Temperatures

Inorg Chem. 2022 Sep 5;61(35):13700-13707. doi: 10.1021/acs.inorgchem.2c00480. Epub 2022 Aug 23.

Authors

Masao Kita¹, Issei Suzuki², Noriyuki Wada³, Takahisa Omata²

Affiliations

¹ Department of Mechanical Engineering, National Institute of Technology, Toyama College, 13 Hongo-machi, Toyama 939-8630, Japan.
² Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
³ Department of Materials Science and Engineering, National Institute of Technology, Suzuka College, Shiroko-cho, Suzuka 510-0294, Japan.

PMID: 35998340
DOI: 10.1021/acs.inorgchem.2c00480

Abstract

The thermal stability and high-temperature phase transformation of metastable Cu₂ZnGeO₄ were investigated in an Ar atmosphere by thermogravimetry, differential thermal analysis, and high-temperature X-ray diffraction. Three Cu-deficient Cu^I_2-xZnGeO_4-2/x phases with a wurtzite-related structure were observed, with varying amounts of copper deficiency. The metastable Cu₂ZnGeO₄ was stable at approximately 275 °C and transformed into intermediate phases. The intermediate phases had a wurtz-kesterite structure with a small number of copper and oxygen vacancies, which later transformed into a high-temperature phase at approximately 425 °C. The crystal structure of the high-temperature phase was assumed to be a deficient wurtzite-related structure with hexagonal closely packed oxygen and deficient copper sites on the order of tens of a percent. The high-temperature phase decomposed into stable Cu₂O, GeO₂, and Zn₂GeO₄ phases above 550 °C. The mechanism for the formation of the phase with a large amount of copper deficiency is discussed, leading to an understanding of the formation process for the copper-deficient phase of complex compounds containing monovalent copper.