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We investigated the phase transitions of CaF2, using the state-of-the-art density functional theory. The calculations show that the fluorite structure, with the space group Fm 3 ¯ m , transforms into the cotunnite structure, with the space group Pnma, at 8 GPa. The electronic band structure of the Pnma-CaF2 structure can be classified as an insulating phase with a wide bandgap, and the bandgap decreases under pressure above 70 GPa. Also, we proposed the Ca/Mg-substituted fluorides MgxCa1-xF2, using the cluster expansion technique which is commonly used to study alloys. We found that the Mg0.25Ca0.75F2 compound with a Pm structure is stable at 70 GPa. The results of the electronic band structure reveal that the substitution of Mg enhances the bandgaps of the Mg0.25Ca0.75F2 compounds under pressure above 70 GPa, compared with those of CaF2.

The action of ultrashort laser pulses on dielectrics leads to the processes of redistribution of the laser pulse energy in the interaction region. The mechanisms of ultrafast energy deposition and the electron dynamics under the action of ultrashort laser pulses determine the type of final structures or elements in the transparent dielectrics. One type of these elements is a birefringent nanogratings formed with an orientation perpendicular to the laser radiation. In this work, laser-induced birefringent structures in calcium fluoride (CaF2) bulk were obtained under the action of tightly-focused laser pulses with durations 0.3-3.8 ps and wavelengths of 515 and 1030 nm. Birefringence in modified region was analyzed using polarization contrast optical microscope with Abrio imaging system.

In this paper, a Self-consistent Orthogonalized linear combination of atomic orbitals (OLCAO) technique with a generalized gradient approximation such as Perdew–Burke–Ernzerhof Solid (GGA-PBE SOL) has been used to scrutinize the structural, optical, electronic and mechanical properties of normal pressure phase (Anatase and Rutile) and high pressure phase i.e., cubic (Fluorite and Pyrite) TiO2. Electronic and optical properties of normal pressure phases of TiO2 are also investigated using (Meta) MGGA-Tran and Blaha (TB09) and obtained results are a close approximation of experimental data. It is seen that the virtually synthesized structural parameter for cubic and tetragonal phases of TiO2 are consistent with experimental and theoretical data. From the effective mass of charge carriers (m*), it can be observed that pyrite TiO2 is having lower effective mass than the fluorite and hence shows higher photocatalytic activity than fluorite. Furthermore, it is seen that fluorite is more dense than anatase, rutile and pyrite TiO2. From the theoretical calculations on the optical properties, it can be concluded that optical absorption occursin the near UV region for high and normal pressue phases of TiO2. Again from the reflectivity characteristics R(ω), it can be concluded that TiO2 can be used as a coating material. Elastic constants, elastic compliance constants, mechanical properties are obtained for anatase, rutile, fluorite and pyrite TiO2. A comparison of the results with previously reported theoretical and experimental data shows that the calculated properties are in better agreement with the previously reported experimental and theoretical results.

We report the crystal structure of Nd–Fe alloys as candidates for grain-boundary phases in Nd–Fe–B sintered magnets. We find that the crystal structure of the fluorite Nd–Fe alloys is stable for a wide composition range. We also demonstrate that solid solution of Ga is effective in stabilizing the fluorite crystal structure of Nd–Fe alloys, which is consistent with experimental observations reporting crystalline Nd–Fe alloys at the grain boundaries of Ga-added Nd–Fe–B permanent magnets.

The effect of introduction of 0.5 – 2 mol.% Yb2O3 additional doping oxide into ZrO2 – 10 mol.% Sc2O3 solid solutions on the phase composition, structure and electrophysical properties has been studied. ZrO2 stabilization due to the joint effect of 10 mol.% Sc2O3 and 2 mol.% Yb2O3 provides for the formation of transparent homogeneous crystals with a cubic structure having high phase stability. Mechanical grinding of the crystals has not changed their phase composition, the powders retaining the initial fluorite crystalline structure. We show that the high-temperature electrical conductivity of the crystals decreases with an increase in the Yb2O3 concentration.

In the production of fluorspar (fluorite) of various grades, the rapid and accurate determination of fluorite is important. The chemical method is used as a marking method, and neutron activation analysis is used as an express method. Initially, the neutron-activation analysis method for fluorite was used by V. Ya. Bardovski for well logging. Its essence is reduced to the irradiation of rocks containing CaF2, a neutron flux from the polonium-beryllium source, followed by the measurement of induced activity on the short-lived isotopes 16N and 20F. This method has the following advantages in comparison with chemical: expressiveness and relatively simple analysis technique, the ability to determine very small amounts of individual elements in rocks and the possibility of element-by-element analysis of rock composition in natural occurrence. The results obtained from the studies indicate that a plutonium-beryllium source should be given preference. According to calculations by E M Filippov [10], 50% of oxygen using a polonium-beryllium source is equivalent to 0.025% fluorine, and for plutonium-beryllium it is 0.0085%.

The optical characteristics of two Russian-made CaF2 ceramic samples are compared to those of single-crystal CaF2. The results indicate that the ceramic possesses high optical quality and a small absorption coefficient (~10-3 cm-1 at a wavelength of 1.07 μm) and is suitable as a material for optical components. Experimental evidence is presented for spatial modulation of the thermally induced depolarisation in the ceramic.

The behaviour of high-purity fluorite and KU-1, KS-4V and Corning 7980 quartz glasses exposed to an electron beam and KrF laser radiation is studied. Exposing these materials to ~5-MW cm-2 KrF-laser radiation both during the action of the electron beam and after it reduces their residual absorption at least by a factor of 1.5.

Efficient room-temperature high-order Stokes and anti-Stokes steady-state generation in two wide-used host-crystals LuVO4 and CaF2 for lanthanide lasants has been discovered. All recorded χ(3)-lasing components are identified to the SRS-promoting phonon modes of these crystals. We classified lutetium vanadate and fluorite as media for promising for up- and down-Raman laser-frequency converters, as well as for self-SRS lasers.

We report molecular dynamics simulations of the production of radiation cascades in pyrochlores. We consider the apparently similar systems Gd2Ti2O7, Gd2Zr2O7 and Gd2Pb2O7, the first two of which have been put forward as potential materials for high-level radioactive waste storage. The effects of changing the mass of the 'primary knock-on' atom are also examined and we investigate whether the change in behaviour from Ti to Zr to Pb is largely due to the mass or the size difference between the elements. Problems associated with analysing the cascades and the damage created are discussed. There are clear differences between the three compounds. The simulations see no direct amorphization but rather a transition to the fluorite structure which is more pronounced for the Zr and Pb compounds than the Ti system. Underlying chemical trends are examined.

Highest purity calcium difluoride crystals having a roughness below 1 nm over large areas were prepared by ultra-precision machining to create technical surfaces for optical applications. High resolution dynamic scanning force microscopy reveals surfaces with close to atomic flatness over areas larger than 10 µm2. The residual roughness is due to a high density of pits and protrusions with a height of 0.32 nm corresponding to an F–Ca–F triple-layer that is the smallest possible unit on stoichiometric CaF2(111). Additionally, imperfections of the machining process may appear as protrusions of typically 1 nm height or a high density of aligned triple-layer steps for surfaces that were apparently slightly inclined with respect to the machining plane. A terraced structure also appears in the vicinity of nanometre-sized defects found for one sample. Machining may also cause a fracture in the form of branched channels of some tens of nanometres in width and some micrometers in length.

In some future interferometric gravitational wave detector projects, LCGT and EGO, the mirrors will be cooled so as to reduce the thermal noise. In order to evaluate the thermal noise of such cryogenic interferometers, the mechanical loss of the reflective coating of the mirrors was measured at low temperature. The measured loss angles were about 4 × 10−4 and constant between 4 K and 300 K. This result implies that the thermal noise of the coating is proportional to the square root of the temperature. The cooling mirror suppresses the thermal noise of the coating loss effectively, which satisfies the goal sensitivity of the future projects (h ~ 3 × 10−24 Hz−1/2 at 100 Hz). The Q-values of fluorite, which is a candidate for the mirror substrate of the cryogenic interferometer, were also measured at low temperature. The measurement showed that the Q-value below 12 K is at least 107. The fluorite mirrors must be cooled down to less than 5 K if they are to be used in future projects.

Recent advancement in liquid-environment atomic force microscopy (AFM) has enabled us to visualize three-dimensional (3D) hydration structures as well as two-dimensional (2D) surface structures with subnanometer-scale resolution at solid-water interfaces. However, the influence of ions present in solution on the 2D- and 3D-AFM measurements has not been well understood. In this study, we perform atomic-scale 2D- and 3D-AFM measurements at fluorite-water interfaces in pure water and a supersaturated solution of fluorite. The images obtained in these two environments are compared to understand the influence of the ions in solution on these measurements. In the 2D images, we found clear difference in the nanoscale structures but no significant difference in the atomic-scale contrasts. However, the 3D force images show clear difference in the subnanometer-scale contrasts. The force contrasts measured in pure water largely agree with those expected from the molecular dynamics simulation and the solvent tip approximation model. In the supersaturated solution, an additional force peak is observed over the negatively charged fluorine ion site. This location suggests that the observed force peak may originate from cations adsorbed on the fluorite surface. These results demonstrate that the ions can significantly alter the subnanometer-scale force contrasts in the 3D-AFM images. © 2017 IOP Publishing Ltd., Embargo Period 12 months

The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO2 have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO2. Compared with the energy band structure of pure CeO2, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO2 were explained through the absorption spectra and the selection rule of the band-to-band transitions.

The pressure-induced sequence of phase transitions of the BaF2 fluorite was studied within the shell-model approach. This fluorite crystal presents two pressure-induced phase transitions at approximately 3 and 15 GPa. The interatomic potentials were calculated by using relevant physical properties measured at ambient conditions. These potentials were used to minimize the lattice enthalpy at high hydrostatic pressures. By comparing the enthalpies and lattice parameters of the three possible structures, it was possible to describe the complete phase transition sequence of the material. The model reliability is confirmed by a comparison with experimental results reported at ambient conditions, which are in good agreement with the model predictions.

We have investigated the high-temperature superionic transition of the anion-excess fluorite with x = 0.06 using both monochromatic and time-of-flight Laue single-crystal neutron diffraction. The measured Bragg intensities indicate that the cuboctahedral defect clusters found at ambient temperature start to break up into smaller fragments even below the superionic transition temperature, . Information concerning the local defect configuration at T = 1173 K has been provided by modelling the measured distribution of the coherent elastic diffuse scattering within the plane of reciprocal space. The high-temperature defects are of the `Willis' type and strongly resemble the short-lived Frenkel clusters found in the pure fluorites such as above .

Chromium-doped and have been studied by both EPR and ENDOR spectroscopy. ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: , , , and for ; and , , , , and for . For , the weak superhyperfine interaction of with the surrounding ions has been studied by both EPR and ENDOR techniques for . No ENDOR signals were detected for . The results are tentatively explained in terms of a Jahn - Teller effect corresponding to coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.

Fluorite structured oxides are used in numerous applications and as such it is necessary to determine their materials properties over a range of conditions. In the present study we employ molecular dynamics calculations to calculate the elastic and expansivity data, which are then used in a thermodynamic model (the cBΩ model) to calculate the activation volumes of oxygen self-diffusion coefficient in ThO2, UO2 and PuO2 fluorite structured oxides over a wide temperature range. We present relations to calculate the activation volumes of oxygen self-diffusion coefficient in ThO2, UO2 and PuO2 for a wide range of temperature (300–1700 K) and pressure (−7.5 to 7.5 GPa).

The diffusion mechanisms and migration characteristics of point defects in the fluorite structures of UO2 and (U, Pu) O2 were analyzed. The possibility of complex migration mechanisms of anionic and cationic vacancy and interstitial Frenkel defects depending on the stoichiometry of materials was shown.The statistical analysis of published data on the radiation-enhanced diffusion (RED) characteristics of metal atoms in UO2 and (U, Pu)O2 for temperatures 1303-1673 K was carried out. An approximate temperature dependence of RED coefficient was obtained. Within the framework of understanding of the mechanisms of diffusion processes in fluorite structure, the approximate temperature dependence of the RED coefficient of oxygen for UO2 and (U, Pu)O2 was proposed.

The theoretical analysis of the electronic structure of ZrO2 containing oxygen vacancies and calcium ions is carried out. The electronic band-structure calculations for zirconium dioxide in the cubic fluorite structure containing oxygen vacancies and calcium ions are made according to the LMTO method. The values of the total and partial densities of states are calculated. The results are used for the analysis of charge transfer between the components. Mainly an ionic character of bonding for all systems investigated is found.

The behaviour upon compression of fluorite, CaF2, has been determined to pressures of 9 GPa at room temperature by single-crystal X-ray diffraction. The room temperature isothermal bulk modulus, KT, is 81.0+or-1.2 GPa, and K'=5.22+or-0.35. These data are combined with other thermodynamic data to provide a high-pressure, high-temperature equation of state for fluorite.

The anion-excess fluorite (Sr,Y)Cl2.03 has been studied by coherent diffuse neutron scattering techniques. At ambient temperature the disorder is found to be static within instrumental resolution. The parameters of defect cluster models have been fitted directly to the data. Excess chlorine ions are found to aggregate into cuboctahedral clusters whose ionic coordinates agree with those calculated from a simple hard sphere model. At elevated temperatures the scattering exhibits quasi-elastic energy broadening indicating the dynamic nature of the disorder. Data obtained at 1050 K show that the cuboctahedral clusters have broken up, the scattering being reminiscent of that obtained from pure fluorites in the fast-ion phase. It is possible to account for the high temperature scattering in terms of 'snapshot' models of the diffusing anions and their associated relaxation fields.

The observed zero-field splitting parameter D of the triplet self-trapped excitons in alkali fluorides is negative, while in alkaline-earth fluorides of the fluorite structure it is of comparable magnitude but positive. D in these materials is almost completely due to spin-spin interaction. Analysis of D allows an estimate of the separation between the hole and electron charges. These are found to be in satisfactory agreement with the results of recent calculation which predicted the off-centre character of the self-trapped exciton in alkali halide crystals. As for the alkaline-earth fluorides with the fluorite structure, the analysis explains the positive sign of D in this structure and also identifies which of the proposed nearest-neighbour F-H pair configurations corresponds to the observed self-trapped exciton.

The accuracy of the special quasirandom structure (SQS) approach for modeling the structure and energetics of fluorite-structured oxide solid solutions with aliovalent cation substitutions is assessed in an ionic-pair potential study of urania and ceria based systems mixed with trivalent rare-earth ions. Mixing enthalpies for SQS supercells containing 96 and 324 lattice sites were calculated using ionic pair potentials for U0.5La0.5O1.75, U0.5Y0.5O1.75, Ce0.5La0.5O1.75, Ce0.5Y0.5O1.75, and Ce0.5Gd0.5O1.75, which all have stoichiometries of pyrochlores. The SQS results were compared to benchmark values for random substitutional disorder obtained using large supercell models. The calculations show significant improvement of the mixing enthalpy for the larger 324 site SQS, which is attributed to a better description of the structural distortions, as characterized by the radial distribution functions in relaxed systems.

Intracavity investigations were made of a soft (apodised) aperture made by photooxidation of Pr2+ in γ-ray-coloured CaF2 : Pr under the influence of argon laser radiation. This aperture reduced the divergence and increased the output energy of single-mode YAG : Er3+ radiation, compared with the case when a hard aperture was used.

This paper studies two specific procedures for analyzing mining samples through a neutron activation technique called DGNAA (Delayed Gamma Neutron Activation Analysis). This particular study is part of a broader line of research, whose overall objective is to find the optimal procedure for analyzing the fluorite content of samples taken from different parts of a fluorite concentration plant, using the DGNAA method [1-2]. The mining sample is fluorspar, which contains other minerals in addition to fluorite, such as silica, barite, iron oxides and silicates. The main contribution of the article is the development of a new method for determining the fluorite content in minerals and the increase of sensitivity in respect to the symmetrical method and single-cycle activation.

The synthesis and optical properties of cerium oxide (CeO2) nanoparticles by a simple, cost-effective and environment-friendly method using cerium(III) acetate hydrate and lemongrass plant extract. The CeO2 nanoparticles having sizes of 10–40 nm were obtained by calcining the precursors in air at 400, 500, and 600 °C, for 2 h. Results from X-ray diffraction (XRD), and Raman spectroscopy indicated that the synthesized CeO2 nanoparticles have the fluorite structure of the bulk CeO2 samples. The PL intensity of CeO2 increases with increasing calcination temperature. The CeO2 sample calcined at 600 °C shows a stronger emission spectrum than the CeO2 samples calcined at 400 and 500 °C, suggesting its better crystalline and optical properties than the other samples.

Single crystal and optical ceramic CaF2 samples are studied by the method of thermally induced depolarisation of laser radiation at 1076 nm. The absorption coefficients of the single crystal and ceramics are estimated as α < 4.5×10-4 cm-1 and α < 1.33×10-3 cm-1, respectively.

The process of double oxide Dy2O3-HfO2 nanocrystallites formation upon annealing to 1600°C was investigated with the combination off few X-ray and synchrotron methods. XRD and PDF show the mean crystal structure to be fluorite typical for the compounds of Ln2O3-MeO2 type. The ordering of structure and the growth of nanocrystallites upon annealing was estimated independently from XRD patterns, PDF functions and SAXS scattering curves. Neither transition to pyrochlore phase, nor signs of recently shown in related Gd2O3-HfO2 compounds pyrochlore-type superstructure is observed. However, EXAFS and the short range order of PDF clearly indicate the discrepancy between Dy and Hf local environment. Such a disorder of local crystal structure cannot be described by the fluorite model.

Using intensive optical absorption techniques we studied formation of lithium nanoparticles in LiF crystals under 60Co-?-irradiation in the dose range of 105?109 R at 300 K. At 106 R the F-center absorption band 4.95 eV grows up D>3 and splits into a symmetric doublet of narrow resonances similar to s1-metal nanoparticles surface plasmons. The maximal concentration 3.3?1017 cm?3 corresponds to ~14 nm distance between F-centers when they form F-F-pair and then M-center. Absorption band of divacancies 2.75 eV splits into triplet at > 107 R, when Lin nanoparticles 3.26 eV are formed. Twinned LiF lattice provides the defects ordering and assembling of Lin nanorods with the size of 8 nm related with the peak electric conductivity at 240?280 K.

A series of ceria-zirconia containing terbia samples were prepared by coprecipitation, and were characterized by XRD, Raman spectroscopy and UV-vis diffuse reflectance measurements. A single-phase solid solution with a cubic fluorite-type structure or tetragonal distorted fluorite structure was obtained for the samples heated at 900°C. Diffuse reflection spectra of the powders showed a broad band at 320-340 nm, which is assigned to interband transitions of CeO2 in the UV region. The effect of ZrO2 on the interband and absorption band of CeO2 was investigated in a series of solid solutions.

Ceria-zirconia solid solution powders were prepared by coprecipitation method. The products were characterized by XRD, colorimetric assessment, and UV-Vis diffuse reflectance measurement. The mixed phase powders were obtained for a series of ZrxCe1−xO2 having the CeO2-rich and ZrO2-rich phase belongs to cubic fluorite structure. Diffuse reflectance spectra of the powder in the UV region show the broad shoulder-type band at 320–340nm, which is assigned to interband transitions in CeO2. The most absorption of visible light and the most vivid yellow pigment colour were observed for x = 0.6 in ZrxCe1−xO2.

The internal friction in three cubic zirconias, Zr0.8R0.2O1.9 where R=Y, Nd and Sm, was compared in the temperature range of 30-400°C using forced torsion pendulum method. The internal friction of Zr0.8Y0.2O1.9 was characterized to two peaks, however that of Zr0.8Sm0.2O1.9 were shown with low amplitude of high temperature peak, as well as that of Zr0.8Nd0.2O1.9 was shown as a single peak at around 100-300°C at 9Hz. The comparative result suggests the effect of the larger cation doping to cubic zirconia, which induced to suppress some kind of oxygen relaxation in cubic fluorite structured zirconia.

The frequency dependences of the dielectric constant (εr') for the oxide-ion conductor Ce0.7Yb0.3O2-δ with two types of electrode, Pt and La0.6Sr0.4FeO3-δ (LSF), were successfully explained by the superposition of polarizations due to charging currents and Debye-type dipoles of the dopant–vacancy associates, [YbCe'–VO ••]• and [YbCe'–VO ••–YbCe']×. The magnitudes of polarizations of the associates were very large for the sample with the Pt electrode, but were smaller by one or two orders of magnitude for the sample with the LSF electrode. The bulk and grain-boundary resistivities in the impedance spectra of Ce0.7Yb0.3O2-δ, which ought to be invariable regardless of the type of electrode used, showed a large difference between the samples with Pt and LSF electrodes. As a result, the impedance spectra were also explained by the Debye-type dipoles of the dopant–vacancy associates.

The electrical conductivity and dielectric properties of the Zr0.8Ln0.2O1.9 (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) system which have a cubic fluorite-type structure were investigated in order to clarify a dynamic property of oxygen vacancy in oxide-ion conductors. The frequency dependences of dielectric constants (r') were successfully explained by the superposition of Debye-type polarizations and electrolyte-electrode interfacial polarizations. The ac conductivity (σac) agreed with the calculated values using the dielectric parameters. It was found that the compositional dependence of dielectric properties was similar to that of σac.

We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant, bulk modulus and cell volume per unit formula are consistent with the available theoretical data. Moreover, the pressure-induced phase transition of OsN2 from pyrite structure to fluorite structure has been obtained. It is found that the transition pressure of OsN2 at zero temperature is 67.2 GPa. The bulk modulus B as well as other thermodynamic quantities of fluorite OsN2 (including the Gr?neisen constant ? and thermal expansion ?) on temperatures and pressures have also been obtained.

Ferromagnetic nanowires (NWs) of Fe–Co silicide have been formed successfully by the codeposition of Fe and Co onto a clean Si(110) surface at 750 °C in an ultrahigh vacuum (UHV). NWs up to 3.0 µm long are self-aligned along the Si[110] direction, owing to the low symmetry of the ideal Si(110) surface. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) reveal that NWs have a fluorite structure including both Fe and Co. Electron holography (EH) reveals that the magnetization of an NW is perpendicular to its long axis and is ca. 0.6±0.1 T at room temperature (RT).

Among three intermetallic compounds existing in Y-Mn system the YMn2 and Y6Mn23 can easily form interstitial hydrides while for YMn12 existence of hydride has never been reported. At moderate hydrogen pressure YMn2 and Y6Mn23 transform into YMn2H4.5 and Y6Mn23H25 respectively. At high hydrogen pressure the YMn2 (C15 or C14 parent structure) forms a unique YMn2H6 (s.g. Fm3m) complex hydride of fluorite structure in which one Mn atom Mn(1) and Y randomly occupy the 8c sites while second manganese (Mn2) in position 4a forms complex anion with 6 hydrogen atoms located in positions 24e. Formation of YMn2H6 independently of the structure of parent phase (C14 or C15) as well as occupation of the same site (8c) by Y and Mn(1) atoms suggested that also Y6Mn23 and YMn12 could transform into YMn2H6 – type hydride in which suitable number of Y atoms will be substituted by Mn(1) in the 8c positions. This assumption was confirmed by exposing R6Mn23 and RMn12 to 1 GPa of hydrogen pressure at 1000C. Formation of (RxMn2−x)MnH6 (where x = 18/29 or 3/13 for R6Mn23 and RMn12 hydrides respectively) was confirmed by XRD. Hydrogen concentration in both R6Mn23 and RMn12 based hydrides reached H/Me = 2 thus value two times higher than in R6Mn23H25.

Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds - stannate and stannate- zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd2Zr2O7) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 °C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn 4+ substitution for Zr 4+ reduces production temperature and the compounds REE2ZrSnO7 may be hot-pressed or cold pressed and sintered at ~1400 °C. Pyrochlore, A2B2O7-x (two-fold elementary fluorite unit cell), and murataite, A3B6C2O20-y (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C - murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt.% AnO2 (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C → 8C → 3C phases with the highest actinide concentration in the core and the lowest - in the rim of the grains. Radiation resistance of the "murataite" is comparable to titanate pyrochlores. One more promising actinide hosts are ferrites with garnet structure. The matrices containing sometime complex fluorite structure oxide as an extra phase have leach and radiation resistance similar to the other well-known actinide waste forms.

An investigation of structural stabilities, electronic and optical properties of SrF2 under high pressure is conducted using a first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results predict that the second high-pressure phase of SrF2 is of a Ni2In-type structure, and demonstrate that the sequence of the pressure-induced phase transition of SrF2 is the fluorite structure (Fm3m) to the PbCl2-type structure (Pnma), and to the Ni2In-type phase (P63/mmc). The first and second phase transition pressures are 5.77 and 45.58 GPa, respectively. The energy gap increases initially with pressure in the Fm3m, and begins to decrease in the Pnma phases at 30 GPa. The band gap overlap metallization does not occur up to 210 GPa. The pressure effect on the optical properties is discussed.

The synthesis by high energy mechanical activation and structural characterization of the phases of Bi3TiNbO9 are described. A fluorite-like metastable phase was identified upon heating the activated powders in the temperature range of 593 to 823 K, followed by formation of the stable Aurivillius phase above 873 K. The crystallization temperature of the fluorite phase increases with milling time. From Rietveld analysis of X-ray diffraction patterns, the fluorite cell parameter is shown to decrease, while rutile TiO2 increases with milling time

Raman spectrum and angle-dispersive x-ray diffraction (ADXD) measurements have been performed to investigate the effects of high temperature on the high-pressure behavior of bulk CeO 2 . A phase transformation of CeO 2 from fluorite to PbCl 2 -type structure occurs at 12.0 GPa and is completed at 14.2 GPa after the sample is heated, and the phase transition pressure decreases by nearly 20 GPa compared with that at room temperature. On decompression, the high-pressure phase of CeO 2 remains down to 2.2 GPa, and it changes back to a cubic structure at ambient conditions. At a pressure of 22.1 GPa, a 6.4% lattice volume difference between the fluorite and PbCl 2 -type structures was observed. The lattice volume of fluorite phase obtained in the areas that have been heated is about 1% less than that obtained in the areas that have not been heated. Besides prompting the phase transition of CeO 2 , high temperature also anneals the sample and leads a small reduction in lattice volume of the fluorite phase. The zero-pressure bulk modulus of the fluorite phase of CeO 2 after annealing is calculated to be about 200 GPa with an assumed pressure derivative of four, which is smaller than that of former x-ray diffraction experiments at room temperature.

Optimisation of the energy characteristics of a chemical CO laser revealed damage to the optical resonator mirrors. Estimates indicated that when the power density of the incident cw laser radiation was 2–2.5 kW cm-2 the induced thermoelastic stresses could reach the damage threshold of mirrors on fluorite substrates.

We present the use of Raman spectroscopy as a rapid and sensitive means for the phase characterization of ferroelectric SrBi2(Ta1-x Nb x )2O9 (SBTN) thin films. It is shown that frequency shifts, together with Raman selection rules, are characteristic of layered perovskite, fluorite and pyrochlore structures, and thus the Raman spectra can be used as a fingerprint of the symmetry of the examined film. We also find the enormous potential of Raman spectroscopy to detect and quantify fractions of the fluorite and pyrochlore phases coexistent with the SBTN phase.

A Bi-Ta multi-seeding layer system is proposed to improve the ferroelectric properties of SrBi2Ta2O9 (SBT) thin films prepared by a sol-gel method for applications to nonvolatile memories. For seeding layers composed of different ratios of Bi to Ta, three different structures were observed after heat treatment at 800°C: γ-Bi2O3, Bi3TaO7 and Bi1.4Ta2O6.75. γ-Bi2O3 with a sillenite structure exhibited a plate-like surface morphology. Bi3TaO7 with a fluorite structure exhibited a flat surface morphology. Bi1.4Ta2O6.75 with a pyrochlore structure exhibited a rough surface morphology. Because a flat surface morphology with a fluorite structure is desirable for a seeding layer, the Bi–Ta seeding layers, with a Bi to Ta ratio equal to 3 to 1, were used as multi-seeding layers. When the seeding layers were sandwiched between SBT thin films, multi-seeding layers provided, after heat treatment at 800°C, a higher degree of crystal orientation in the a- or b-axis direction than a simple SBT thin film without seeding layers. Orientation in the a- or b-axis direction is desirable for SBT thin films to obtain improved ferroelectric properties, especially high remanent polarization values. The SBT thin film with Bi–Ta multi-seeding layers was found to have higher saturation characteristics than that without seeding layers, which suggests that the former type of SBT thin film has a good potential for low-voltage operation. The multi-seeding method is thus effective for improving ferroelectric properties of SBT thin films for nonvolatile memories.

In the Sr–Bi–Ta–Nb–O system, three crystallographic phases are known to exist: the SrBi2(Ta1-x Nb x )O9 (SBTN) perovskite, fluorite and pyrochlore phases. It is considered that the fluorite phase is a low-temperature phase of SBT, which tends to grow in excess bismuth compositions, and the pyrochlore phase tends to grow in bismuth-deficient compositions. In conventional X-ray diffraction (XRD) characterization, the SBTN phase shows strong (115) diffraction around 29 [2θ deg]. Unfortunately, however, the other two phases also show their (111) and (222) diffractions near the same angle when the film is prepared on a platinum-coated silicon substrate. Therefore, the phase identification of the SBTN phase from the other two phases is almost impossible by the conventional technique. We employed XRD reciprocal space mapping to distinguish these phases in the present study. The three crystallographic phases were identified and distinguished from each other. It is ascertained that this technique is effective to identify crystallographic phases especially in the case in which more than two phases show similar diffraction angles.