Anisotropic Thermal Diffusivity and Conductivity of La‐Doped Strontium Niobate Sr₂Nb₂O₇

Abstract

The thermal diffusivity of the La‐doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000°C. The anisotropy persists through an incommensurate‐normal ferroelectric phase transformation at 215°C and up to 1000°C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05±0.05 W/mK up to 1000°C. Possible explanations for the low thermal conductivity and anisotropy are described.

Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La2Ti2O7

“…The thermal conductivity of La 2 Ti 2 O 7 is nearly temperature independent as reported in the literature for similar PLS compounds (Sr 2 Nb 2 O 7 ). 23 The thermal conductivity for La 2 Ti 2 O 7 was $1.3 W/m K in this work, which was close to that of other layered structured compounds, e.g., Bi 4 Ti 3 O 12 ($1 W/m K). 21 After Sr substitution, the thermal conductivity increased with increasing temperature.…”

“…20,22 Very low and temperature independent thermal conductivity have been reported for polycrystalline layered perovskite compounds like Bi 4 Ti 3 O 12 ($1 W/m K) 21 and Sr 2 Nb 2 O 7 (1.5 W/m K). 23 La 2 Ti 2 O 7 is the member of the perovskite-like layered structure family with general formula A n B n O 3nþ2 . The n in the formula represents the number of octahedral units in the perovskite layers, which in the case of La 2 Ti 2 O 7 , is four.…”

Thermal (Kapitza) resistance of interfaces in compositional dependent ZnO-In2O3 superlattices

“…[http://dx.doi.org/10.1063/1.4809784] Synthetic 1-4 and natural superlattices [5][6][7] have been reported to exhibit very low thermal conductivities, in some cases close to or even below the minimum thermal conductivity. 8 Compositionally dependent superlattices, sometimes referred to as modular or polysomatic series in the mineralogical literature 9 and homologous series in the crystal chemistry literature, 10 offer the opportunity to select the periodicity of phonon scattering interfaces through choice of composition and thereby the overall thermal conductivity.…”

Low temperature hydrothermal synthesis, characterization and optical properties of strontium pyroniobate

“…Sr 2 Nb 2 O 7 is a part of a series having a chemical composition of Sr n Nb n O 3n+2 [22] where n is the number of NbO 6 octahedrons comprising the slab thickness. Only n = 4 and n = 5 members of the series have been observed so far [22][23][24]. By Cooling from above the Curie temperature, [25] Sr 2 Nb 2 O 7 undergoes the ferroelectric phase transition from space group Cmcm to Cmc2 1 , which is commonly referred to as the normal orthorhombic phase.…”