Low-temperature heat capacity and high-temperature thermal behavior of sodium lutetium molybdate phosphate Na<Subscript>2</Subscript>Lu(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

The low-temperature heat capacity of Na₂Lu (MoO₄)(PO₄) was measured by adiabatic calorimetry in the range of 7.47–345.74 K. The experimental data were used to calculate the thermodynamic functions of Na₂Lu (MoO₄)(PO₄). At 298.15 K, the following values were obtained: C _p ⁰ (298.15 K) = 237.7 ± 0.1 J/(K mol), S ⁰(298.15 K) = 278.1 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰ (0 K) = 42330 ± 20 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0. 3 J/(K mol). A heat capacity anomaly was found in the range of 10-67 K with a maximum at T _tr = 39.18 K. The entropy and enthalpy of transition are ΔS = 12.39 ± 0.75 J/(K mol) and ΔH = 403 ± 16 J/mol. The thermal investigation of sodium lutetium molybdate phosphate in the high-temperature range (623–1223 K) was performed using differential scanning calorimetry. It was found that during melting in the range of 1030–1200 K, Na₂Lu(MoO₄)(PO₄) degrades to simpler compounds; the degradation scenario is verified by X-ray powder diffraction.     

Complex potassium yttrium molybdate phosphates K2Y1 ? xEux(MoO4)(PO4)0.9(VO4)0.1: Synthesis and study of luminescent properties

Samples with various dopant contents were obtained using solid-state and sol-gel methods. The resulting single-phase samples have the formula K₂Y_{1 − x} Eu _x (MoO₄)(PO₄)_0.9(VO₄)_0.1 (x = 0, 0.005, 0.01, 0.02, 0.03) and are isostructural with K₂Y(MoO₄)(PO₄). The possibility of formation of complex molybdate vanadates M₂^IM^III(MoO₄)(VO₄). was studied. Unlike their precursor K₂Y(MoO₄)(PO₄), the complex potassium yttrium molybdate phosphates obtained are deliquescent. Their structures contain no water molecules. The absorption and emission spectra of the compounds under study were recorded. In all the spectra, the electric dipole transition ⁵ D ₀−⁷ F ₂ (616 nm) is appreciably more intense than the magnetic dipole transition ⁵ D ₀−⁷ F ₁ (590 nm). This suggests that the coordination environment of the Eu³⁺ ion keeps asymmetric. The excitedstate lifetimes of anhydrous and humidified samples were determined. The average lifetime is the same for all samples (≈1.5 ms), which is due to the stability of their structures.     

Refined heat capacity of LaPO4 in the temperature range 0–1600 K

In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO₆ is refined by the Rietveld method: space group F d3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å³. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion.     

New approach to the synthesis of 1,3-dioxolanes

Application of ethanol to the synthesis of 1,3-dioxolanes by the condensation of carbonyl compounds with vicinal diols results in a high yield of the reaction product and considerably reduces the duration of the process. It is assumed that the effect of the ethanol is caused by the adduct formation with carbonyl compounds (hemiacetals) which behave as active intermediates of the condensation. A cyclic ketal of acetone with glycerol obtained with the help of ethanol was used as a basis component in the synthesis of a series of ketals substituting diol or carbonyl components by transketalyzation mechanism proceeding without water liberation.     

On the structure and dehydration of hydrous zirconia and hafnia xerogels

Hydrous zirconia and hafnia xerogels of compositions ZrO₂ · 2.5H₂O and HfO₂ · 2.3H₂O are dehydrated in two steps upon heating. First, molecular water is mostly removed from the structures to form phases of compositions ZrO₂ · H₂O and HfO₂ · 0.5H₂O. Second, polycondensation of OH groups occurs. Both processes are easier for ZrO₂ · 2.5H₂O. Apart from these steps, the interaction of water molecules with zirconium-oxygen bridges was found to occur during dehydration of the zirconium compound. The composition of HfO₂ · 0.5H₂O should actually read as Hf₄O₇(H₂O)(OH)₂.