Report of the Double-Molybdate Phase Cs2Ba(MoO4)2 with a Palmierite Structure and Its Thermodynamic Characterization

The existence of a novel double-molybdate phase with a palmierite-type structure, Cs 2 Ba(MoO 4 ) 2 , is revealed in this work, and its structural properties at room temperature have been characterized in detail using X-ray and neutron diffraction measurements. In addition, its thermal stability and thermal expansion are investigated in the temperature range 298-673 K using high-temperature X-ray diffraction, leading to the volumetric thermal expansion coefficient α V ≈ 43.0 × 10 -6 K -1 . The compound's standard enthalpy of formation at 298.15 K has been obtained using solution calorimetry, which yielded Δ f H m °(Cs 2 Ba(MoO 4 ) 2 , cr, 298.15 K) = -3066.6 ± 3.1 kJ· mol -1 , and its standard entropy at 298.15 K has been derived from low-temperature (2.1-294.3 K) thermal-relaxation calorimetry as S m °(Cs 2 Ba(MoO 4 ) 2 , cr, 298.15 K) = 381.2 ± 11.8 J K -1 mol -1 .