Z. I. Zhmurova

Mechanochemical Synthesis of Nonstoichiometric Fluorite Ca{sub 1-x} La{sub x} F{sub 2+x} Nanocrystals from CaF{sub 2} and LaF{sub 3} Single Crystals

The nonstoichiometric Ca1−xLaxF2+x phase (x ≥ 0.1) is obtained by mechanochemical synthesis from CaF2 and LaF3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the MFm-RFn systems (m < n ≤ 4). The average grain size ranges within 10–30 nm. The temperature dependence of ionic conductivity of the mechanochemically synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200–250°C) coincides with the conductivity of the single crystals of the same composition (Ca0.8La0.2F2.2). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.

Spectroscopic properties of nonstoichiometric multicomponent fluoride crystals with fluorite structure doped with Pr3+ ions

Abstract Spectral studies of nonstoichiometric multicomponent fluoride crystals, doped with the Pr 3+ ions, which have a CaF 2 -type partially disordered structure have shown that these crystals are promising candidates for amplifiers in the 1.3 μm range. In Ba 1− x R x F 2+ x :Pr crystals the oscillator strengths of all transitions are markedly increased in comparison with those in BaF 2 crystals due to the formation of centres with a low symmetry of their local environment. The concentration quenching of the luminescence in Ba 1− x R x F 2+ x :Pr and Pb 0.67 Cd 0.33 F 2 :Pr crystals as well as the probability of nonradiative relaxation from the 1 G 4 state are smaller than those in glasses.

Optimization of single crystals of solid electrolytes with tysonite-type structure (LaF3) for conductivity at 293 K: 2. Nonstoichiometric phases R1−yMyF3−y (R = La-Lu, Y; M = Sr, Ba)

Single crystals of fluorine-conducting solid electrolytes R1 − ySryF3 − y and R1 − yBayF3 − y (R = La-Lu, Y) with a tysonite-type structure (LaF3) have been optimized for room-temperature conductivity σ293 K. The optimization is based on high-temperature measurements of σ(T) in two-component nonstoichiometric phases R1 − yMyF3 − y (M = Sr, Ba) as a function of the MF2 content. Optimization for thermal stability is based on studying the phase diagrams of MF2-RF3 systems (M = Sr, Ba) and the behavior of nonstoichiometric crystals upon heating when measuring temperature dependences σ(T). Single crystals of many studied R1 − ySryF3 − y and R1 − yBayF3 − y phases have σ293 K values large enough to use these materials in solid-state electrochemical devices (chemical sensors, fluorine-ion batteries, accumulators, etc.) operating at room temperature.

Mechanochemical synthesis of nonstoichiometric nanocrystals La1 − yCayF3 − y with a tysonite structure and nanoceramic materials from CaF2 and LaF3 crystals

The nonstoichiometric phases La1 − yCayF3 − y (y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the compositions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase diagram of the CaF2-LaF3 system. The “mechanohydrolysis” of the La1 − yCayF3 − y phase has been observed for the first time. Under these conditions, the La1 − yCayF3 − y phase partially transforms into lanthanum calcium oxyfluoride for a milling time of 180 min with intermediate sampling. The La1 − yCayF3 − y nanoceramic materials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure of (2–6) × 108 Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature of 200°C is equal to 4.9(6) × 10−4 S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These data for the nanoceramic materials coincide with those obtained for migration of fluorine vacancies in single-crystal tysonite fluoride materials.

Nanostructured crystals of fluorite phases Sr1 − xRxF2 + x (R = Y, La-Lu) and their ordering: Part III. A study of the refractive indices

The refractive indices n of Sr1 − xRxF2 + x crystals (R = Y, La-Lu; 0 ≤ x ≤ 0.5) have been measured at wavelengths of 0.436, 0.546, and 0.589 μm. It is established that n increases when there is an increase in the RF3 content x according to a weakly quadratic law for each R. For the isoconcentration series of Sr0.9R0.1F2.1 crystals, the change in n in the series of rare earth elements has a pronounced nonlinear character, which reflects the nonmonotonous change in the properties of compounds in the R series. It is shown that the method of molecular refraction additivity can be used to calculate n for Sr1 − xRxF2 + x crystals. By varying the RF3 content in them, one can obtain optical media with a gradually varied refractive index n in the range 1.44–1.55, thus filling the gap in the n values between high ones for RF3 crystals and low ones for crystals of alkaline earth fluorides MF2.

Nanostructured crystals of fluorite phases Sr1 − xRxF2 + x (R are rare earth elements) and their ordering: 5. A study of the ionic conductivity of as-grown Sr1 − xRxF2 + x crystals

The ionic conductivity σ of Sr1 − xRxF2 + x crystals (R = Y, La-Lu) has been measured in the temperature range of 324–933 K. The isomorphic introduction of R3+ ions into SrF2 is accompanied by an increase in conductivity up to four orders of magnitude, which makes these crystals superionic conductors. It is shown that the conduction mechanism in Sr1 − xRxF2 + x crystals changes when passing from R = La-Nd to R = Sm-Lu. A change in the type of cluster of structural defects between Nd and Sm is suggested. The concentration dependences of σ and the activation energy of charge-carrier migration (Ea) for Sr1 − xRxF2 + x are nonlinear. For crystals with R = La or Nd, these dependences are interpreted within the percolation model of “defect regions,” the minimum size of which is estimated to be ∼700 Å3. It is shown that the electrical properties of the crystals can be controlled by varying the RF3 type and concentration. The Sr1 − xRxF2 + x crystals (R = La-Nd, 0.3 ≤ x ≤ 0.5), for which σ = (2−3) × 10−2 S/cm at 673 K and Ea = 0.6−0.7 eV, have the best electrolytic characteristics.

The amplification and excited state absorption of Nd-doped nonstoichiometric crystals with fluorite structure in the 1.3 μm region

Abstract The spectroscopic characteristics in the 1.3 μm region of nonstoichiometric fluorite phases M 1- x R x F m (1- x )+ nx , doped by Nd 3+ ions were investigated. The direct measurement of excited state absorption and amplification in 1.3 μm region were carried out. The halfwidth of amplification spectrum in Na 0.5- x Y 0.5+ x F 2+2 x and Ca 1- x Y x F 2+ x crystals was found to be less than that the halfwidth of the luminescence spectrum due to excited state absorption (ESA). The maxima of amplification bands are located at ∼1365 nm with halfwidth of ∼40 nm for Na 0.5- x Y 0.5+ x F 2+2 x crystals and ∼60 nm for Ca 0.9 Y 0.1 F 2.11 crystals. The maximum values of effective cross sections σ eff =σ em -σ esa for these crystals are 2.2 ± 0.7 × 10 -21 cm 2 and 4.5 ± 0.9 × 10 -21 cm 2 , respectively.

293-K conductivity optimization for single crystals of solid electrolytes with tysonite structure (LaF 3 ): I. Nonstoichiometric phases R 1−y Ca y F 3−y ( R = La-Lu, Y)

The systematic optimization of single-crystal fluoride-conducting solid electrolytes R1 − yCayF3 − y with a tysonite type structure (LaF3) with respect to the conductivity at room temperature, σ(293 K), is based on high-temperature measurements of σ(T) of stoichiometric fluorides of rare earth elements, RF3 (R = La-Nd), in dependence of the radius

Investigation of multicomponent fluoride optical materials in the UV spectral region: I. Single crystals of Ca1−xRxF2+x (R = Sc, Y, La, Yb, Lu) solid solutions

R^{3 + } (r_{R^{3 + } } )