Positive muons in SrTiO; Electronic structure of the hydrogen-like defects and their potential use in depth-resolved detection of oxygen vacancies

SrTiO中の正ミュオン; 水素様欠陥の電子構造解析および酸素空孔分布の深さ分解測定への応用の可能性

伊藤 孝   ; 髭本 亘  ; 幸田 章宏*; 下村 浩一郎*

Ito, Takashi; Higemoto, Wataru; Koda, Akihiro*; Shimomura, Koichiro*

Recent SR studies in SrTiO focusing on the following two aspects will be presented. (i) Electronic structure of interstitial Mu in SrTiO: The formation of a Mu-Ti polaron complex was observed upon implantation of positive muons into stoichiometric SrTiO. The small activation energy of 30(3) meV found for the thermal dissociation of the Mu-Ti polaron complex suggests that the strain energy required to distort the lattice is comparable to the electronic energy gained by localizing the electron. (ii) Potential use of SR for oxygen vacancy detection in SrTiO: The oxygen vacancy (V) is a major defect species in perovskite titanates, having a strong impact on their electrical, optical, and dielectric properties. In spite of the importance of the defect, experimental techniques that can directly detect V are still limited. Through a series of SR measurements on oxygen-deficient SrTiO we revealed that there is a clear positive correlation between the muon spin relaxation rate and the carrier concentration, which is expected to be roughly proportional to the V concentration. This, together with the variability of muon implantation depth, suggests that the SR spectroscopy is potentially suitable for the depth-resolved analysis of V distribution in perovskite oxides, which is complementary to cation vacancy-sensitive techniques, such as positron annihilation spectroscopy.