0000000000024796
AUTHOR
O. B. Shcherbina
Physical and Chemical Principles of Obtaining Thermally Resistant Containers for Treatment of High Purity Niobium and Tantalum Compounds
Mathematical modelling of the distribution of strain in layered quartz ceramics with protective coating of niobium (tantalum) pentoxide from two sides is reported. It is found that fragmentation of the basic layer (decreasing the area of the continuous boarder between layers) and smoothing of sharp edges of the base fragments should reduce the strains on the boundary between the substrate and coating and, correspondingly, enhance the thermal resistance of the samples. Treatment of the niobium pentoxide coating by concentrated light induces a network of fractal micro- and nano-size fractures that compensates the difference of thermal expansion between the layers.
Growth of Lithium Niobate Single Crystals from Granulated Charge
Comparative studies of different techniques and the synthesis of single-phase granulated mixtures of high density essentially improving technical and economical parameters of lithium niobate single crystal technology are reported. Efficiency of using granulated mixtures of high density in growing lithium niobate single crystals is discussed.
Effects of VTE Treatment on Composition of Lithium Tantalate Single Crystals
The vapour transport equilibration (VTE) is used to change the Li/Ta ratio in lithium tantalate single crystals of different crystallographic orientations (Z-cut and Y/128°-cut). Treatment by VTE is shown to provide thin layers in lithium tantalate plates composition of which is close to stoichiometric while the values of the coercive field are different, much smaller compared with congruent single crystals. There are several mechanisms of diffusion of the Li+ ions in LiTaO3 under conditions of VTE the contribution of each being dependent on the crystallographic orientation of the sample.
The Effect of Grain Size of the Stock on Electrical Characteristics of the Li0.03Na0.97Ta0.05Nb0.95O3Perovskite Ceramics
The microstructure and electrical properties of two samples of the ferroelectric Li0.03Na0.97Ta0.05Nb0.95O3 ceramic solid solution prepared from initial charge stocks of different dispersity by conventional ceramics technology are compared. The average size of grains and concentration of pores in the samples are found to be of little difference while the electrical properties of the ceramics are strongly affected by the grain size of the initial mixture. The difference in properties is due to conditions at the diffusion stage of the solid-phase synthesis caused by differences in composition of larger grains rather than the grain size itself.
FRACTAL STRUCTURES IN SINGLE CRYSTALS OF FERROELECTRIC LITHIUM NIOBATE GROWN UNDER STRONGLY UNSTABLE CONDITIONS
Atomic force microscopy studies of lithium niobate single crystals containing heterogeneously distributed lanthanide (Gd) admixture and a regular domain structure of 100 nm to 1 μm steps obtained under conditions of severe thermal instability have revealed fractal structures of the size of 10 to 100 nm within regions of the regular domain structures. A super-structure of clustered defects with 1–2 nm steps explaining results of Raman spectra analysis is supposed to exist in the cation sub-lattice and formation of periodic fractal structures of the size of ∼1 nm–100 μm is suggested to take place in lithium niobate single crystals containing lanthanide admixture.
MICRO- AND NANO-STRUCTURES IN SINGLE CRYSTALS OF LITHIUM NIOBATE CONTAINING LANTHANIDE ADMIXTURES
ABSTRACT Micro-size domain structures in lithium niobate single crystals containing lanthanide (Gd, Tm, Sm, Lu) admixture, grown under stationary and non-stationary conditions are studied by efficient and flexible Thixomet® image analyser. Regular fractal-type domain structures observed along the three Y-axes of the hexagonal crystallographic set-up are assigned to pinning of the domain walls at defects created under conditions of imbalanced crystallization of the doped melt. Characteristic types of domains have been found analysing the configurations of domains on optical and atomic force microscopic images of surfaces of different crystallographic orientations.
FORMATION OF FRACTAL MICRO- AND NANO-STRUCTURES IN CERAMIC TANTALUM PENTOXIDE UNDER CONCENTRATED FLUX OF LIGHT AND THEIR EFFECT ON THERMAL EXPANSION
ABSTRACT Oxides of weak thermal expansion are the basis for stable ceramics and artefacts resistant to sharp cyclic variations of temperature. For technical applications is a wide interest in high-temperature materials of low or negative thermal expansion and, particularly, in studies of the micromechanisms in Ta2O5. Thermal expansion of ceramic pentoxides of tantalum is affected by conditions under which they are formed. After treatment by concentrated light flows anomalous segments of zero and even negative thermal expansion appear in ceramics of Ta2O5. The effect of treatment by concentrated light flux on formation of fractal nano-structures and thermal expansion of ceramic tantalum pent…
Formation of Layers of Diverse Stoichiometric and Phase Composition in Lithium Tantalate Crystals at Treatment by Vapour Transport Equilibration
Layers from tens to hundreds of microns thick of a different phase composition and stoichiometry are shown to form in lithium tantalate crystals subjected to treatment by vapor transport equilibration in lithium vapour. The 500 microns thick stoichiometric (Li/Ta ≈ 1) layers have ten times lower values of the coercive field compared with congruent lithium tantalate. As electrical measurements suggest, a new polar structure of phase transition at ∼120°C is possibly formed within a thin (30 μm) surface layer of the lithium tantalate sample after vapour transport equilibration treatment.