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

Abstract

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 .

Structural Studies and Thermal Analysis in the Cs2MoO4–PbMoO4 System with Elucidation of β-Cs2Pb(MoO4)2

“…b Note that the statistically derived standard uncertainties obtained from the refinement were underestimated by about 1 order of magnitude and were thus multiplied by 10, as listed in this table. and ND refined profile parameters of Cs 2 Ba(MoO 4 ) 2 by Smith et al 8 The discrepancy, which is about the same on the three axes, might be explained by a slight deviation in the neutron wavelength or from a refinement artifact. A temperature difference during the measurement cannot account for the order of magnitude of this observation.…”

“…The structural family of binary molybdates and tungstates shows appealing properties, for instance, ferroelastic and ferroelectric behavior. , Among these complex compounds is a group of binary molybdates and tungstates with mono- and bivalent elements, i.e., the A 2 + B 2+ (X 6+ O 4 ) 2 structural type, with A = K, Rb, or Cs, B = Ba and Pb, and X = Mo and W. ,− Moreover, binary molybdates and tungstates are also versatile as host materials for phosphors. , …”

Minerals with a palmierite-type structure. Part II. Nomenclature and classification of the palmierite supergroup.

“…The palmierite supergroup includes five mineral species, defined chemically as sulfates, phosphates and vanadates (Table 1). According to the data on synthetic analogues and their structure type, this supergroup may also include chromates, molybdates, selenates, arsenates and wolframates (Morris et al, 1977;Chance and Loye, 2013;Tsyrenova et al, 2016;Bismayer et al, 2017;Smith et al, 2020).…”