Anisotropic thermal conductivity of the Aurivillus phase, bismuth titanate (Bi4Ti3O12): A natural nanostructured superlattice

Abstract

The thermal conductivity of c-axis textured polycrystalline perovskite Bi4Ti3O12 and random polycrystalline material is reported up to 1000 °C. Based on measurements of the thermal diffusivity, density, and specific heat, the thermal conductivity is lower along the c-axis than in the a-b plane by almost a factor of 2, and the anisotropy persists up to at least 1000 °C despite a change in the crystal structure at 675 °C. The exceptionally low (1.0 W/mK), temperature-independent conductivity perpendicular to the perovskite layer structure is attributed to the density difference between the pseudoperovskite and fluorite blocks in the unit cell, forming a natural nanostructured superlattice.

Optical anisotropy in bismuth titanate: An experimental and theoretical study

“…It is interesting to note that anisotropy in different physical properties have different origins. For example, directional dependence of thermal properties is attributed to the density difference between the perovskite and the fluorite type (Bi 2 O 2 ) layers in the unit cell 25 while anisotropy in the electrical properties arises due to differences in the oxygen vacancy concentrations in the perovskite and Bi 2 O 2 oxide layer of the structure. 23,26 In contrast, anisotropy in the ferroelectric polarization is attributed to non-zero displacement of Ti ions along a-axis.…”

“…4 At Curie temperature (T c ¼ 948 K), ferroelectric BiT transforms into a paraelectric phase with centrosymmetric tetragonal (I4/mmm) structure having lattice parameters, a ¼ b ¼ 3.8524 Å and c ¼ 33.197 Å . 23 Noncentrosymmetry of the room temperature structure along with its complexity further renders anisotropic physical properties in the material, namely dielectric constant (e a ¼ e b ¼ 153 6 5 and e c ¼ 118 6 5 at 100 kHz), 6 ferroelectric polarization, 15,24 and thermal 25 and electrical 23,26 conductivities. It is interesting to note that anisotropy in different physical properties have different origins.…”

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

“…16 They consist of multiple layers of perovskite units separated by systematic layers. 20,21 For this reason, the layered perovskite structured compounds exhibit anisotropic and anomalously low thermal conductivity values compared to the perovskite structured compounds. 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).…”

“…20,21 For this reason, the layered perovskite structured compounds exhibit anisotropic and anomalously low thermal conductivity values compared to the perovskite structured compounds. 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 .…”

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.…”