High-temperature thermoelectric properties of Sr 2RuYO 6 and Sr 2RuErO 6 double perovskites influenced by structure and microstructure

Abstract

The high-temperature thermoelectric properties of Sr 2RuYO 6 and Sr 2RuErO 6 double perovskites were evaluated and reported for the first time. These compounds show high Seebeck coefficients not only at room temperature, but also at high temperature (for Sr 2RuYO 6, S RT ≈ −475 μV K −1 and S 1200K ≈ −250 μV K −1; Sr 2RuErO 6, S RT ≈ −400 μV K −1 and S 1200K ≈ −250 μV K −1). The n-type semiconducting behaviour dominates the resistivity values. Both compounds crystallize in a monoclinic unit cell (space group P2 1/ n). The lattice parameters are a = 5.7761(2), b = 5.7804(1), c = 8.1689(1), α = γ = 90° and β = 90.2087(8)° for the Sr 2RuYO 6, and a = 5.7760(1), b = 5.7722(0), c = 8.1544(4), α = γ = 90° and β = 90.2099(7)° for Sr 2RuErO 6. The unit cell can be described approximately as √2 a p × √2 a p × 2 a p, where a p is the unit cell parameter of the ideal cubic perovskite structure. High-resolution transmission electron microscopy shows an interesting three-dimensional micro-twin-domain texture where the c axis is placed in the three space directions. Structural transitions at high temperatures ( T t(Sr 2RuYO 6) ≈920 K and T t(Sr 2RuErO 6) ≈890 K) are observed by specific heat measurement in both compounds, which are found to have a strong influence on the Seebeck coefficient and electrical conductivity.