[en] In this article authors studied thermic stability of tantalic bromide,the pressure of saturated vapor of TaBr₅ also passed the measuring ofunsaturated vapor

[en] Na₂Ta₄O₁₁ crystallizes rhombohedrally in the space group R3c with a = 6.198 3 and c = 36.56 2 A. The structure was determined by single crystal X-ray diffraction and refined with 164 reflexions to R = 0.048. It contains like Na₂Nb₄O₁₁ layers of pentagonal tantalum oxygen bypyramids, which are connected by octahedrally coordinated tantalum atoms

[en] The luminescence of perovskite-like niobates and tantalates is compared and discussed in connection with that of titanates. The luminescence properties are strongly related to each other. Electronic delocalization in corner-sharing octahedra is shown to play an important role

[en] Attempts have been made to elucidate some probable mechanism for basic medium condensation process in heteropoly niobates and tantalates. (auth.)

No abstract available

[en] Return to disorder, and less frequently memory, have been demonstrated in various disordered materials. In order to find the conditions necessary for the observation of these effects, the evolution of the real part ε' of the dielectric constant of two disordered paraelectric crystals K_1-xLi_xTaO₃ (KLT) has been extensively studied by the means of the capacitance C (T, t) around the beginning and the end of a temperature plateau. The return to disorder and memory effects have not been seen in KTL, in contrast to what was recently observed in disordered ferroelectric crystals KTa_1-yNb_yO₃ of a similar family. The variations dC = P (T₀, t₀) dT + Q (T₀, t₀ ) dt in the vicinity of the point (T₀, t₀) are split into a contribution depending on temperature only and an isothermal contribution only depending on time. All the results of such an analysis of the features observed in KLT can be explained by the domain wall model in its original form. (author)

[en] Measurement of absorbance along the z-axis of a lithium tantalate crystal was completed using a Cary spectrophotometer. Transmission through two polished but uncoated faces was about 62% which compares well with 73% calculated from Fresnel reflectivity equations

[en] Optical absorption, photo- and X-ray luminescence spectra are studied of GdTaO₄ monocrystalline are studied of GdTaO₄ monocrystallione matrix and also when introducing activators. Differencies are revealed between the GdTaO₄ monocrystal X-ray luminescence and its photoluminescence

No abstract available

[en] This thesis presents the results of investigations into the thermal and optical control of ferroelectric domains within lithium tantalate and strontium barium niobate crystals. The aim of the work was to develop techniques for optically patterning domain inverted structures within ferroelectric crystals. Initial studies involving strontium barium niobate revealed an enhanced temperature sensitivity for transient repoling occurring at room temperatures for this material. This has important consequences for the optical manipulation of domains in this material. Further work indicated that the optical control of domains in this material were limited by the variation in crystal properties of strontium barium niobate crystals. Subsequent work concentrated on lithium tantalate, in which domain patterning was successfully accomplished at room temperature via the simultaneous application of optical and electric fields. The technique consisted of illuminating the x-face of a 200 μm thick lithium tantalate z-cut crystal which had been polished to form a biprism. The resulting interferometric pattern, formed between planar electrodes applied to the +z and -z crystal faces, had a period of ∼6 μm. This optical pattern defined where poling occurred by effectively increasing the coercive field within the illuminated regions of the crystal. This effect was used to inhibit ferroelectric switching within the illuminated regions so that the optical pattern is thereby translated into a corresponding domain structure. The increase in coercive field is a consequence of internal field relaxation within the crystal, for which the underlying principles of light induced ferroelectric switching are addressed. This is the first demonstration of optical periodic domain patterning using interferometric techniques. (author)