Radiographic methods for elemental analysis of boron,lithium, radium,uranium and thorium in minerals and rocks

The feasibility is discussed of applying different radiation sources for f-radiography, (n, α)-radiography and autoradiography for the determination of the spatial distribution, and the local and total concentrations of boron, lithium, radium, uranium and thorium in various materials, achieving high sensitivity and accuracy. Results demonstrating the application of the developed methods of radiography in geological practice are presented.     

Mechanism and nature of phase transitions in the (NH4)3MoO3F3 oxyfluoride

The temperature dependences of the heat capacity, the unit cell parameter, and the permittivity for the (NH₄)₃MoO₃F₃ cryolite (space group Fm $ \overline 3 The temperature dependences of the heat capacity, the unit cell parameter, and the permittivity for the (NH₄)₃MoO₃F₃ cryolite (space group Fm m) are investigated. It is revealed that the compound undergoes ferroelectric and ferroelastic structural phase transitions at temperatures of 297 and 205 K, respectively. The mechanism of structural distortions is discussed in terms of the entropy parameters, pressure-temperature phase diagrams, and electron density maps for critical atoms. An analysis is made of the influence of the cation size and shape on the phase transitions in oxyfluorides of the general formula A ₂ A′MO₃ (A,A′ = NH₄, K; M = Mo, W). Original Russian Text ? I.N. Flerov, V.D. Fokina, A.F. Bovina, E.V. Bogdanov, M.S. Molokeev, A.G. Kocharova, E.I. Pogorel’tsev, N.M. Laptash, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 3, pp. 497–506.     

Effect of Isovalent Cation Substitution on the Thermal,Caloric, and Magnetocaloric Properties of the (La1 – yEuy)0.7Pb0.3MnO3 Manganites

Physics of the Solid State - Crystalline samples of the (La1 – yEuy)0.7Pb0.3MnO3 (y = 0, 0.2, 0.4, 0.5, 0.6, and 0.8) manganite solid solutions have been grown. Temperature...     

Phase transitions in the (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>NbOF<Subscript>5</Subscript> oxyfluoride

The thermal and dielectric properties of the (NH₄)₂NbOF₅ oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc2₁ → C2 → Ia observed at the temperatures T ₁ = 258.0 K and T ₂ = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of the phase transitions.     

Thermal expansion of (Ba1 ? xLax)Ti1 ? x/4O3 solid solutions

Deformation and the thermal expansion coefficient of ceramic samples of (Ba_{1 − x} La _x )Ti_{1 − x/4}O₃ solid solutions (x = 0, 0.026, 0.036, 0.054) were studied in the temperature range 120–700 K. Based on an analysis of the data obtained, the temperature-composition phase diagram is refined, and the temperature dependence of the polarization is calculated. The results are discussed in combination with the dielectric measurement data. Original Russian Text ? M.V. Gorev, I.N. Flerov, Ph. Sciau, S. Guillemet-Fritsch, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 4, pp. 746–752.     

Ferroelastic phase transition in elpasolite Tl2KInF6

A new elpasolite Tl₂KInF₆ has been synthesized. This compound undergoes at 228 K a ferroelastic phase transition from a room-temperature Fm3m variety to a monoclinic variety. X-ray, optical, calorimetric and DTA studies under hydrostatic pressure have been performed and compared with other elpasolite-type fluorides.     

Low-temperature specific heat of the Rb<Subscript>2</Subscript>KScF<Subscript>6</Subscript> elpasolite

The specific heat of single-crystal Rb₂KScF₆ is measured using ac calorimetry in the range 4–280 K. The results are discussed in the context of a group-theoretical analysis of possible distortions of the elpasolite structure and of experimental data obtained earlier with an adiabatic calorimeter in a narrower temperature region.     

Studies of the thermodynamic properties of the ordered perovskites Pb2CdWO6 and Pb2YbTaO6 within a broad temperature range

This paper reports on measurements of the specific heat of Pb₂CdWO₆ made at temperatures ranging from 80 to 750 K and of Pb₂YbTaO₆ within the 350-to 700-K temperature range. First-order phase transitions from the cubic phase at 677.3 and 581 K, respectively, were observed, and their thermodynamic characteristics were determined. The entropy change on the phase transitions is close to Rln4 for both compounds. The results obtained are discussed in terms of the model of position disordering of the lead ions. It was established that below 350 K, Pb₂CdWO₆ can exist in two states, stable and metastable, depending on the sample thermal prehistory.     

Calorimetric and x-ray diffraction studies of the (NH4)3WO3F3 and (NH4)3TiOF5 perovskite-like oxyfluorides

The heat capacity and unit cell parameters of the (NH₄)₃WO₃F₃ and (NH₄)₃TiOF₅ perovskite-like oxyfluorides were measured in the temperature interval from 80 to 300 K; the existence of two and one phase transitions in these compounds, respectively, was demonstrated, and their thermodynamic parameters were determined. The effect of a hydrostatic pressure of up to 0.5 GPa on the phase transition temperatures was studied. Triple points and high-pressure phases were found in the T vs. p diagrams. An analysis of entropy changes suggests that all the structural transformations revealed are associated with the ordering of structural blocks. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 5, 2004, pp. 888–894. Original Russian Text Copyright ? 2004 by Flerov, Gorev, Fokina, Bovina, Laptash.     

Thermodynamic properties of the mixed elpasolites Rb2KGaxSc1−x F6 (x=0.6–1.0)

Measurements of the heat capacity of the elpasolite Rb₂KGaF₆ and the solid solutions Rb₂KGa_xSc_1−x F₆ with a gallium content in the range x=0.6–0.95 are performed. The nature of the influence of the chemical composition of the compounds and the hydrostatic pressure on the temperature and entropy of the ferroelastic phase transitions is established. Fiz. Tverd. Tela (St. Petersburg) 39, 1844–1849 (October 1997)