P. P. Fedorov

Phase diagrams of thE CaF2- (Y, Ln) F3 svstems I. Experimental

Abstract The phase diagrams of the CaF 2 - (Y, Ln) F 3 systems, where Ln is any one of the lanthanides except Pm and Eu, were studied by thermal and X-ray phase analysis methods. The investigations were made from 800 (600)°C up to the melting temperature. The oxygen concentration of the specimens was checked after thermal treatment. For the systems with Ln = Ce, Pr, Tb, Ho, Tm and Lu the fusibility data have been obtained for the first time. Phases with the following structure types are present in the systems investigated: (a) solid solutions Ca 1− x (Y, Ln) x F 2+ x with the fluorite structure type, which undergo ordering in the systems with Ln = HoLu, Y; (b) non-stoichiometric phases (Y, Ln) 1− y Ca y F 3− y with the tysonite (LaF 3 ) structure type, which undergo ordering in the systems with Ln = TbLu, Y; (c) solid solutions with the α-UO 3 structure type, based on α modifications (Y, Ln) F 3 (Ln = ErLu); and (d) modifications (Y, Ln) F 3 (Ln = GdLu) of the β-YF 3 type. Successive transitions, from solid solutions of the components of the system to the berthollide phases and the stoichiometric compound, were found for phases with the tysonite structure type. The maxima on fusion curves of non-stoichiometric phases were noticed in Sm, Gd, Tb, Ho and Er for Ca 1− x - (Y, Ln) x F 2− x and for Ln = PrLu in (Y, Ln) 1− y Ca y F 3− y . The coordinates of non-variant points for equilibria of the liquid-solid type and also the equations describing the dependence of the lattice parameters of nonstoichiometric phases on the composition are given for the systems investigated.

Efficient laser based on CaF 2 -SrF 2 -YbF 3 nanoceramics

CaF(2)-SrF(2)-YbF(3) fluoride ceramics of high optical quality was prepared, and its absorption, fluorescence, and laser oscillation properties were investigated. Oscillation slope efficiency that was only a few percent lower than that for a single crystal of similar composition was demonstrated under diode pumping.

On the problem of polymorphism and fusion of lanthanide trifluorides. II. Interaction of LnF3 with MF2 (M = Ca, Sr, Ba), change in structural type in the LnF3 series, and thermal characteristics☆

Abstract The results of a study on the interaction of Ln F 3 with M F 2 ( M = Ca, Sr, Ba) for 34 binary systems of the Ln F 3  M F 2 type in the concentration range 60–100 mole % Ln F 3 are presented. It is shown that in this range the interaction of the components in the Ln F 3  M F 2 systems is similar to that in the Ln F 3  Ln 2 O 3 systems. The problem of stabilizing different structural types of Ln F 3 (tysonite and α-YF 3 ) during the isomorphous substitution of Ln 3+ by M 2+ and 2F − by O 2− with formation of solid-solid solutions Ln 1− x M x F 3− x and Ln F 3−2 x O x , respectively, is discussed also. In congruent fusion of these phases, the coordinates of the maximum on the fusibility curve (according to composition) are regularly displaced to the side of pure Ln F 3 with a decrease in the atomic number of the lanthanide. The vacancy-stabilized phases are typical examples of variable composition compounds (berthollides). On the basis of data on the interaction of components in the Ln F 3  Ln 2 O 3 and Ln F 3  M F 2 systems, problems of polymorphism and changes of structural type in the Ln F 3 series are discussed. Fusion and polymorphic transformation temperatures are given for Ln F 3 with control of oxygen content in the specimens after thermal analysis.

On the problem of polymorphism and fusion of lanthanide trifluorides. I. The influence of oxygen on phase transition temperatures

Abstract The details of using thermal analysis (TA) in the investigation of lanthanide trifluorides are examined. By examining the literature on the problem of phase transitions in LnF3 (Ln = lanthanum and the lanthanides), it is established that the basic reason for disagreement among the data of various authors is, in most cases, lack of control of pyrohydrolysis of LnF3. For the first time, parts of the phase diagrams of the LnF3Ln2O3 systems (Ln = Gd, Tb, Ho, Er, and Y) have been studied with TA methods. Phases LnF3−2xOx where 0 ≤ x ≤ 0.2, which were not known earlier, are discovered. According to the type of interaction of LnF3 with the corresponding Ln2O3, the trifluoride series is broken down into several groups corresponding to the structural type in which the LnF3 crystallizes. The parts of the phase diagrams of the LnF3Ln2O3 systems that were studied permit us to explain the reasons for contradictions in existing data on the temperatures of phase transformations in LnF3.

Phase diagrams of the SrF2(Y, Ln)F3 systems part I.—X-ray characteristics of phases

Abstract The phase equilibria in the subsolidus part of 14 binary systems of SrF2(Y, Ln)F3 type (Ln—all lanthanides except Pm and Eu) were studied at temperatures over 850°C in equilibrated and quenched specimens by the X-ray analysis method. The oxygen concentration in the specimens before and after the thermal treatment was checked. The crystallographic characteristics of phases formed in the systems i.e. nonstoichiometric phases Sr1−xLnxF2+x with fluorite type structure, phases with fluorite derived type structure, nonstochiometric phases Ln1−ySryF3−y with tysonite (LaF3) type structure are given in this paper.

Oriented attachment of particles: 100 years of investigations of non-classical crystal growth

The results of investigations of non-classical crystal growth by the oriented attachment mechanism are summarized. The data published since the end of the 19th century are considered, the attention being focused on analysis of publications of the last 15 years. Data on characteristic features of the oriented attachment of particles are described systematically. The experimental methods used to elucidate the peculiarities of non-classical crystal growth, including in situ methods, are discussed. The prospects of application of the oriented attachment of particles for the formation of various materials are demonstrated.The bibliography includes 227 references.

CdF2:In: A novel material for optically written storage of information

We demonstrate that semiconducting CdF2 crystals doped with indium is an efficient medium for optical storage of information in static and dynamic regimes. A metastable phototransformation of 1018 cm−3 In centers from a localized deep state to a hydrogenlike shallow state leads to a change of the refractive index Δn of about 10−4 for the probe beam at the wavelength of 500 nm. The diffraction efficiency is temperature dependent due to spontaneous decay of the grating caused by thermal recovery of the In impurity from the metastable hydrogenic state to the localized ground state.

Specific features of ion transport in nonstoichiometric Sr1−xRxF2+x phases (R=La, Y) with the fluorite-type structure

Abstract Temperature and concentration dependence of ionic conductivity (δ) was studied for the crystals of nonstoichiometric Sr 1− x R x F 2+ x phases (R=La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu, Y;0 x ⩽0.40) having the fluorite structure ( Fm 3 space group). The temperature dependence of σ of the crystals in the region 300–800 K obeys the Arrhenius equation. In order to explain the ion transport features observed (absolute σ and ΔH σ values, their concentration dependence) in the anion excess solid solutions, a model of “defect regions” is proposed. Within the framework of the model, the conductivity of a solid solution is determined by the ratio of the conductivities of the “defect region” and the matrix. It is shown that in relation to electrical characteristics, the whole set of nonstoichiometric phases can be divided into three groups, R=La, Ce, Pr, Nd: R=Gd, Tb, Dy, Ho; R=Er, Lu, Y. This division correlates well with a number of other crystallophysical and crystallochemical characteristics. The average concentration of charge carriers (F − ) and their average mobility in the Sr 0.8 R 0.2 F 2.2 crystals were calculated: n =2.2×10 27 m −3 , μ 500 K =2.8×10 −11 m 2 / s/V for solid solutions with R=La, Ce, Pr, Nd and n =6.8×10 26 m −3 , μ 500 K =3×10 −14 m 2 / sV for solid solutions with R=Er, Lu, Y.

Thermal conductivity of single crystals of Ca1 − xYbxF2 + x solid solutions

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca1 − x Y x F2 + x with the fluorite structure (x ≤ 0.20) and the Ca0.27Y0.73F2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.

Thermal conductivity of single crystals of the Ca 1 − x Y x F 2 + x solid solution

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca1 − x Y x F2 + x with the fluorite structure (x ≤ 0.20) and the Ca0.27Y0.73F2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.