Lighter Sr doping engineering the lattice anharmonicity in Ba1−xSrxSnO3−δ

Abstract

The synergistic effects of the oxygen vacancies and Sr doping on the lattice dynamics of perovskite Ba_1−xSr_xSnO_3−δ (x = 0, 0.03, 0.06, 0.10) are systematically investigated through neutron powder diffraction, Raman scattering, specific heat capacity, and thermal conductivity measurements, combined with thermal-transport theoretical calculations. The introduction of the defects induces local distortions and unique vibrational behaviors, and has been observed by different measurements. The existence of the oxygen vacancies activates several Raman spectra that are otherwise not active in vacancy-free BaSnO₃, and the Sr doping further introduces more Raman excitations. On heat capacity, the defect-induced optical phonons enhance the intensity of the Boson peak and move the peak value to a lower temperature region. Furthermore, the defects not only significantly reduce the lattice thermal conductivities (κ_L) by lowering the sound velocity and strengthening the lattice anharmonicity, but also cause the temperature-independent κ_L due to the large contribution of the coherent thermal conductivity. This work establishes a structure-dynamics-transport relationship in the defect-engineered perovskite oxides and paves the path to achieve intrinsically low thermal conductivity in other materials.