Thermal Expansion and Phase Transitions in Na₃H(SO₄)₂ Sulfate in the Low-Temperature Range

N. V. Dmitrieva^a, R. S. Bubnova^a^,^b^, *, S. K. Filatov^a, A. P. Shablinskii^a^,^b, and M. G. Krzhizhanovskaya^b

^aGrebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, 199034 Russia

^bSt. Petersburg State University, St. Petersburg, 199034 Russia

Correspondence to: *e-mail: rimma_bubnova@mail.ru

Received 16 November, 2018

Abstract—The thermal behavior of Na₃H(SO₄)₂ is studied in the temperature range –180...220°C in a pre-vacuum. At 180°C, the compound decomposed into a mixture of phases: Na₂SO₄ (Cmcm), Na₂SO₄ (P6₃/mmc), Na₂SO₄ (Fddd), and Na₂S₂O₇. The maximal thermal expansion was observed near the α₃₃ axis. The anisotropy of thermal expansion sharply decreased together with the increase in temperature.

Keywords: sulfates, high temperature X-ray diffraction, thermal expansion, phase transitions

DOI: 10.1134/S1087659619050043

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Thermal Expansion and Phase Transitions in Na₃H(SO₄)₂ Sulfate in the Low-Temperature Range