Site-Selective Oxygen Vacancy Formation Derived from the Characteristic Crystal Structures of in Sn-Nb complex Oxides

TL;DR

This study investigates how the crystal structure of Sn-Nb complex oxides influences oxygen vacancy formation, which affects hole mobility and efficiency in p-type oxide semiconductors, using advanced spectroscopy and structural analysis.

Contribution

It reveals the relationship between crystal structure and oxygen vacancy formation, highlighting the importance of local Sn-O bonding for material design to enhance p-type oxide semiconductors.

Findings

Oxygen vacancies preferentially form at Sn-bonded O sites.

High oxygen vacancy concentration correlates with low hole-generation efficiency.

Differences in Sn-O bond strength influence vacancy formation and are linked to crystal structure.

Abstract

Divalent tin oxides have attracted considerable attention as novel p-type oxide semiconductors, which are essential for realizing future oxide electronic devices. Recently, p-type Sn2Nb2O7 and SnNb2O6 were developed; however, enhanced hole mobility by reducing defect concentrations is required for practical use. In this work, we investigate the correlation between the formation of oxygen vacancy which may reduce the hole-generation efficiency and hole mobility, and the crystal structure in Sn-Nb complex oxides. Extended X-ray absorption fine structure spectroscopy and Rietveld analysis of x-ray diffraction revealed the preferential formation of oxygen vacancy at the O site bonded to the Sn ions in both the tin niobates. Moreover, a large amount of oxygen vacancy around the Sn ions were found in the p-type Sn2Nb2O7, thereby indicating the effect of oxygen vacancy to the low hole-generation efficiency. The dependence of the formation of oxygen vacancy on the crystal structure can be elucidated from the Sn-O bond strength that is evaluated based on the bond valence sum and Debye temperature. The differences in the bond strengths of the two Sn-Nb complex oxides are correlated through the steric hindrance of Sn2+ with asymmetric electron density distribution. This suggests the importance of the material design with a focus on the local structure around the Sn ions to prevent the formation of oxygen vacancy in p-type Sn2+ oxides.