Muon spin relaxation in mixed perovskite (LaAlO\(_3\))\(_{x}\)(SrAl\(_{0.5}\)Ta\(_{0.5}\)O\(_3\))\(_{1-x}\) with \(x\simeq 0.3\)

We report on muon spin relaxation ( \({\mu ^+}\) ${\mu }^{+}$ SR) measurements in a mixed perovskite compound, (LaAlO \({_3}\) ${}_3$ ) \({_{x}}\) ${}_x$ (SrAl \({_{0.5}}\) ${}_{0.5}$ Ta \({_{0.5}}\) ${}_{0.5}$ O \({_3}\) ${}_3$ ) \({_{1-x}}\) ${}_{1-x}$ with \({x\simeq 0.3}\) $x\simeq 0.3$ (LSAT), which is widely used as a single-crystalline substrate for thin film deposition. In zero applied field (ZF), muon depolarization due to the distribution of nuclear dipole fields was observed in the temperature range from 4 K to 270 K. Interestingly, \({\mu ^+}\) ${\mu }^{+}$ SR time spectra in ZF maintained a Gaussian-like feature over the entire range, while the depolarization rate exhibited a monotonic decrease with increasing temperature. This behavior may be attributed to the thermally activated diffusion of muons between a few adjacent sites within a confined space of the angstrom scale, where the motionally averaged local field that each muon experiences can remain non-zero and result in maintaining the Gaussian-like line shape. The spatial distribution of electrostatic potential at lattice interstices evaluated via density functional theory calculations suggests that such a restriction of muon diffusion paths can be caused by the random distribution of cations with different nominal valences in the mixed perovskite lattice.