Superionic phase transition in Rb₄LiH₃(SO₄)₄, Rb₄LiH₃(SeO₄)₄and K₄LiH₃(SO₄)₄single crystals

Abstract

Abstract DTA studies of a new family of ferroelastic crystals of Me4LiH3(XO4)4 stoichiometry revealed at Ts another phase transition in the paraelastic phase, accompanied by an anomalous increase in the capacitance. Complex impedance method was used to study temperature variation of electric conductivity and its anisotropy of Rb4LiH3(SO4)4, Rb4LiH3(SeO4)4 and K4LiH3(SO4)4 single crystals. The bulk conductivity of the crystals varies from 10−6 to 10−4 (ωm)−1 in the temperature range from ∼ 400 K to temperatures below melting. The conductivity σc is ∼ one order of magnitude lower than σa ∽ σb. At Ts the activation energy Wa ∽ Wb decreases from 0.94 – 1.35 eV below Ts to 0.27 –0.28 eV at T > Ts. Comparison of the data with the crystallographic structure allowed us to classify the transition as superionic.