Electrical transport, magnetic, and thermodynamic properties of La-, Pr-, and Nd-doped BaSnO3−δ single crystals

Abstract

Due to outstanding room temperature electron mobility, the wide-gap perovskite semiconductor $\mathrm{BaSn}{\mathrm{O}}_{3}$ is of high current interest. Although $n$ doping with Sb and O vacancies has been reported, most work has focused solely on La doping. Here we report bulk single crystals of $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}{R}_{x}\mathrm{Sn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ with $R=\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Pr}$, and Nd, as well as unintentionally doped $\mathrm{BaSn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$, thus exploring new rare earth (magnetic) dopants in addition to O vacancy doping. Consistent with recent results on epitaxial films, O vacancies are shown capable of generating mid-${10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ Hall electron densities, with single crystal mobilities $\ensuremath{\sim}100\text{--}150\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Despite apparent solubility limits below $\ensuremath{\sim}0.5\phantom{\rule{0.16em}{0ex}}\mathrm{at}.\phantom{\rule{0.16em}{0ex}}%$, Pr and Nd are also shown to be effective $n$ dopants, yielding Hall electron densities $g1\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$, and ambient and low temperature mobilities up to 175 and $430\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, respectively. In contrast to the La-doped case, clear paramagnetism occurs with Pr and Nd doping, allowing for direct estimates of dopant concentrations for quantitative comparison with Hall densities. We show that dopant and Hall densities can be approximately reconciled, but only after accounting for O vacancy doping. Specific heat measurements were also performed, confirming the $\mathrm{BaSn}{\mathrm{O}}_{3}$ Debye temperature, and revealing electronic contributions roughly consistent with reported effective masses. Interestingly, and likely related to crystalline electric field effects, Pr-doped $\mathrm{BaSn}{\mathrm{O}}_{3}$ exhibits large deviations from simple Curie-Weiss susceptibility, and a pronounced Schottky anomaly, which we analyze in detail. These results provide significant insight into doping in $\mathrm{BaSn}{\mathrm{O}}_{3}$, establishing new rare earth magnetic dopants, clarifying the role of O vacancies, and determining dopant concentrations and solubility limits.