Thermodynamic Characteristics of the Sodium Dimolybdate Single Crystal: Enthalpy and Heat Capacity

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发表日期：

2024年1月1日

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N. I. Matskevich,
A. N. Semerikova,
V. D. Grigor’eva,
D. V. Kochelakov,
D. A. Samoshkin,
S. V. Stankus,
S. A. Luk’yanova,
V. N. Schlegel’,
V. P. Zaitsev,
E. N. Tkachev

摘要

Abstract

The standard enthalpy of formation of sodium dimolybdate was determined by dissolution calorimetry based on the measured enthalpies of dissolution of Na₂CO₃, MoO₃, and Na₂Mo₂O₇ in a 0.2 M NaOH solution and the literature data: Δ_fH⁰(Na₂Mo₂O₇, 298.15 K) = −2245.3 ± 6.3 kJ/mol. The lattice enthalpy was calculated using the Born–Haber cycle: –54 730 kJ/mol. The wavelength of luminescence radiation decreased from 650 to 540 nm on passing from sodium molybdate to sodium tungstate, and the lattice enthalpy decreased from –54 730 kJ/mol (Na₂Mo₂O₇) to –49 030 kJ/mol (Na₂W₂O₇). The temperature dependence of the heat capacity of sodium dimolybdate was determined in the temperature range 320–785 K. There are no phase transitions in this range.