Anomalous thermal conductivity of alkaline-earth-metal-substituted EuTiO3 induced by resonant scattering

Abstract

We have investigated thermal conductivities (κ) of polycrystalline Eu1–xAxTiO3 (A = Ca, Sr, Ba, 0 ≤ x ≤ 0.8) bulk materials in the temperature range of ∼ 2 K < T < 1173 K. The EuTiO3 demonstrates anomalous glass-like κ(T) behavior at low temperatures. Partial substitutions with Sr2+ and Ba2+ do not cause a significant change in the κ(T) behavior, while a κ(T) peak, which looks like a manifestation of a typical crystalline solid, appears only in the Ca-substituted samples with an orthorhombic structure when x ≥ 0.4. After excluding the magnetic effects on κ and discussing the possible phonon scattering mechanisms in depth, together with heat capacity Cp measurements and high-resolution X-Ray diffraction characterization, we find that the unusual low κ at low temperatures is attributed to resonant scattering induced by the intrinsic disordered local structure and lattice instability in EuTiO3. Due to the different lattice dynamics of ATiO3, the lattice structure of Eu1–xCaxTiO3 can be regarded as formed by a part-soft (from EuTiO3) part-rigid (from CaTiO3) sublattice. The anomalous κ(T) behavior of Eu1–xCaxTiO3 results from the combined effect of phonon transport between the normal phononic heat transport in the rigid sublattice and the strong damping of heat conduction in the soft sublattice.