Thermopolarization currents in dielectrics

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Read in full from the JETP Letters archive (four pages). Pure, undoped PbMg₁/₃Nb₂/₃O₃ single crystals — centrosymmetric and paraelectric above 273 K, resistivity ~10¹⁴ Ω·cm — cut as 3 × 3 × 8 mm parallelepipeds with Degus-paste electrodes on the long faces; one end at room temperature, the other heated, in vacuum ≈ 10⁻³ Torr. The external-circuit current density follows the rate of change of the end-to-end temperature difference (ΔT up to ≈ 55 K over 8 mm), reverses when the sign of ∇T is reversed (unlike the pyroelectric current of the sample's random unipolarity, which does not), and its maximum is linear in d(ΔT)/dt (Fig. 2), the slope giving a thermopolarization coefficient B₁₁ ≈ 3 × 10⁻¹² C/(cm·K), a polarization of order 10⁻¹⁰ C/cm² at T = 310 K and ∇T = 30 K/cm; Gurevich's estimate B₁₁ ≈ 10⁻¹³ C/(cm·K) is of the same order. The authors attribute the current to the direct thermopolarization effect of Gurevich's theory; a thermal-expansion strain-gradient (flexoelectric) contribution is not considered, so the letter does not by itself separate the two mechanisms.

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