Niobates; vanadates; tantalates (C30B29/30)

Method of etching of oxidic nonlinear dielectric and optical monocrystals

Method of etching of monocrystals is performed in vapours of the mix containing 1 volume part of fluoric and 2 volume parts of nitric acid, while monocrystals are placed above a ceramic crucible or a plastic cup with the mix of acids heated from the room temperature up to 60-70°C within 7-10 minutes. By effect of vapours of mix the domain and dislocation structures in samples are revealed.

Method of obtaining material for high temperature mass-sensitive piezoresonance sensor based on monocrystal of lanthanum-gallium alluminium tantalate

Method of obtaining a material for a high temperature mass-sensitive piezoresonance sensor based on a monocrystal of lanthanum-gallium aluminium tantalate, the composition of which corresponds to formula La3Ta0.5Ga5.5-xAlxO14, where x=0.1-0.3, characterised by the electric resistance not less than 109 Ohm at a temperature of 20-600°C, includes growing of monocrystals from a melt of oxides its component constituents in an atmosphere of an oxidiser-containing inert gas, and additional annealing in air at a temperature of 1050-1150°C for 41-43 hours.

Method of determining molar ratio of li₂o in linbo₃ monocrystals

Method includes exposing a crystal to initial pulsed polarised non-monochromatic radiation in the short-wave infrared region to obtain initial pulsed polarised radiation in the short-wave infrared range and pulsed polarised radiation of a harmonic in the visible range, separating the pulsed polarised radiation of the harmonic in the visible range, conversion thereof into an electrical signal, obtaining a curve of amplitude of the electric signal versus the wavelength of the pulsed polarised monochromatic radiation of a second and overall harmonic, determining therefrom a 90-degree synchronism wavelength, from which the molar content of Li2O in the LiNbO3 monocrystal is determined. The LiNbO3 monocrystal used is a monocrystal in the form of a plane-parallel plate with crystallographic axis Z located in the plane of the entrance face of the crystal, perpendicular to the axis of the optical system.

Method for formation of bidomain structure in single-crystal plates

Electrodes in the form of a system of parallel strings are applied onto two flat-parallel faces of the crystal, which are aligned at the angle of z+36° to the polar axis, wire platinum contracts are connected to electrodes, the assembled cell is placed into a furnace and heated to temperature of phase transition - Curie temperature under action of a heterogeneous electric field, as a result of which two oppositely charged domains of equal volume are formed with a flat domain-to-domain border.

Method of forming polydomain ferroelectric monocrystals with charged domain wall

Method of forming polydomain ferroelectric monocrystals with a charged domain wall involves using a workpiece in form of plate of ferroelectric monoaxial monocrystal of the lithium niobate and lithium tantalate family, which is cut perpendicular to the polar axis, one of the surfaces of which is irradiated with ion flux to form high concentration of point radiation defects in the surface layer, which results in high electroconductivity of the layer, after which an electric field is formed in the plate, directed along the polar axis, the polarity and value of which enable formation of domains on the surface of the plate which is not exposed, and their growth deep into the plate in the polar direction up to the boundary of the layer with high conductivity, which leads formation of a charged domain wall with an irregular shape, wherein the depth of the layer is determined by the value of the energy and dose of ions, and the shape of the wall is determined by the value of the electric field formed.

Composite tantalate of rare-earth elements

Invention relates to novel chemical compounds and can be used in medicine, particularly radiology as an X-ray contrast agent during X-ray examination of various organs. The invention discloses a composite tantalate of rare-earth elements with the formula M1-xM'xTaO4, where 0.01≤x≤0.45; M and M' are elements selected from a group consisting of: yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, as a contrast agent for X-ray diagnosis. The disclosed contrast agent, which provides a high level of X-ray absorption, enables to smoothly and continuously vary the level of absorption with the same quantitative content of the agent owing to change in values of x, i.e., owing to change in the ratio of atoms the first and second elements in the crystal lattice of tantalate.

Procedure for solid phase synthesis of charge for growth of mono crystals of lanthanum-gallium tantalate

Procedure consists in mixing powders of oxides of lanthanum, gallium and tantalate with grain of granulometric dimension in range of 1-5 mcm, in successive heating produced powder-like mixture with controlled rate to temperature of sintering and in conditioning said mixture at this temperature till sintering process is completed. Also, sintering powder-like mixture of oxides is carried out in two stages, so that at the first stage heating from ambient temperature to sintering temperature T1 in the range 1300-1350°C is performed at rate 120-125 degr/hour and conditioned at this sintering temperature during 2.5-3.0 hours with formation of intermediate compounds of LaGaO3, LaTaO4 formula; while at the second stage heating is performed from temperature of sintering T1 to temperature T2 within the range 1440-1450°C at rate 150-155 degr/hour; mixture is conditioned during 3.5-4.4 hours till completion of sintering process forming stoichiometric compound of lanthanum-gallium tantalate La3Ga5,5Ta0,5O14.

Polarisation method of monocrystal of lithium tantalate

Invention relates to industrial production of monocrystals, received from melt by Czochralski method, and can be used during polarisation of ferroelectrics with high temperature Curie, principally lithium tantalate. On monocrystal of lithium tantalate by means of grinding it is formed contact pad, surface of which is perpendicular to optical axis of crystal or at acute angle to it. Monocrystal is located between bottom segmental or laminar platinum electrode and implemented from wire of diametre 0.3-0.6 mm top circular platinum electrode through adjoining to its surfaces interlayers. In the capacity of material of interlayer it is used fine-dispersed (40-100 mcm) powder of crystalline solid solution LiNb1-xTaxO3, where 0.1≤x≤0.8, with bonding alcoholic addition in the form of 94-96% ethyl alcohol at mass ratio of alcohol and powder 1:2.5-3.5. Monocrystal is installed into annealing furnace, it is heated at a rate not more than 70°C/h up to temperature for 20-80°C higher than temperature Curie of monocrystal and through it is passed current by means of feeding on electrodes of polarising voltage. Then monocrystal is cooled in the mode current stabilisation at increasing of voltage rate 1.2-1.5 times up to temperature up to 90-110°C lower than temperature Curie, and following cooling is implemented in the mode of stabilisation of polarising voltage at reduction of current value through monocrystal. At reduction of current value 3.0-4.5 times of its stable value voltage feeding is stopped, after what monocrystal is cooled at a rate of natural cooling-down. Monocrystal cooling up to stop of feeding of polarising voltage is implemented at a rate 15-30°C/h.

Method of growing doped crystals of lithium niobate with composition close stoichiometric, and device to this end

Invention relates to the technology of growing monocrystals using Chokhralsky method. Growth of doped crystals of lithium niobate with composition close to stoichiometric is done on an inoculating crystal from molten mixture of lithium niobate of identical composition with ratio Li/Nb equal to 0.938-0.946 and containing 9-13 mol % K2O and 0.5-2.5 mol % MgO or ZnO, in conditions of applied electric field with current density of 0.2-40 A/m2. A device is provided for realising the method, comprising a housing with a growth station and a cooling chamber, crucible 1, placed in the growth station, induction heater, top metallic heating shield 4, fitted above the crucible 1, mechanism for moving the crystal with a coupling rod, a rod with a holder 3 for the inoculating crystal 2. The device is also provided with a regulated direct current source 10 with electrodes; under the inoculating crystal 2 there is an additional load from electrically conducting material, separated from the wall of the holder by electrically insulating material. One of the electrodes is connected to the crucible 1, and the second - to the load.

Method of single crystals linbo₃ production and device for its implementation

Invention is related to technology of single crystals LiNbO3 production of stoichiometric composition, which is used in non-linear optics. Single crystals LiNbO3 are melted incongruently, therefore, for production of single crystals of stoichiometric composition, single crystal pulling is used from liquid phase of eutectic composition with make-up of solid phase of preliminarily synthesised compound, which is heated from bottom and top by double-layer spiral electric heater, which is immersed in liquid phase and installed with gap in respect to making-up solid phase, and reduction of temperature gradients in liquid phase and in produced single crystal is performed by application of furnace for single crystal heating. Device includes mechanism of single crystal pulling, thermally insulated crucible with make-up solid phase, flat heater of crucible with thermal insulation, double-layer spiral electric heater with cross-section of spirals in the form of reverse chutes that overlap all section of crucible, which is installed with gap in respect to make-up solid phase, at that double-layer spiral electric heater is equipped with electrodes that pass through furnace thermal insulation for single crystal heating and are fixed to it. Device heaters form flat isothermal surfaces along crucible height, double-layer spiral electric heater with cross section of spirals in the form of reverse chutes that overlap all section of crucible, removes air bubbles that are produced during dissolution of make-up solid phase, from crystallisation front to crucible walls, installation of double-layer spiral electric heater with gap in respect to make-up solid phase provides its heating up to temperature of dissolution provided that temperature gradients in liquid phase and single crystal are reduced, which is achieved by application of furnace with thermal insulation for heating of pulled single crystal, which enters the crucible as make-up dissolves and single crystal is growing.

Device for monocrystal growing of refractory metal oxides

Device includes housing with growing chamber and with cooling chamber mutually divided by means of ceramic partition, crucible arranged in growing chamber, induction heater, upper metallic heating shield mounted over crucible, mechanism with rod for moving crystal. Crucible is in the form of cylinder whose flat bottom is joined with cylindrical lateral surface along spherical surface. Metallic upper shield has two sections, lower cone section and upper spherical section. Between chamber for growing and chamber for cooling diaphragm with changeable concentric inserts is arranged. Induced Foucault current detector in the form of cylinder is mounted on bottom part of crucible. Inner diameter of any concentric insert of said diaphragm exceeds by 2 - 16 mm diameter of grown crystal. Concentric inserts of diaphragm are made of crucible material. Relation of height of cylindrical wall of crucible to height of wall of induced Foucault current detector is in range 2 - 10. Relation of height of cone section of upper metallic shield to height of spherical section of said shield is in range 2 - 5. Apparatus allows grow large-size (with diameter and length more than 100 mm) oxide crystals (LiNbO3, LiTaO3 and others) of high optical quality and excellent structure quality.

Method of production of charge for growing monocrystals on base of oxides of rare-earth metals, trace metals and refractory metals or silicon

Proposed method includes mixing of starting oxides at stoichiometric ratio of components, heating the mixture at rate of 30-350°C/h to temperature of 1460-1465°C and sintering at this temperature for 6.5-8.0 h. Mixing of starting oxides may be performed at application of vibrations at frequency of 50-100 Hz and amplitude of 3-5 mm. Synthesis is carried out in alundum sleeves on whose inner surfaces layer of gallium oxide is applied. Proposed method makes it possible to obtain the charge of homogeneous phase and stoichiometric composition. Yield of phase being synthesized is practically 100%.

Monocrystal with calcium gallogermanate structure for manufacture of disks in devices on surface-acoustic waves and method of production of such crystal

Used as monocrystal with calcium gallogermanate structures in units on surface acoustic waves is monocrystal whose geometric axis is perpendicular to thermostable shear; such monocrystal is grown by Chohralsky method with seed crystal oriented in direction perpendicular to thermostable shear. Proposed monocrystal increases number of disks up to 80% fully free from growth defects-gas bubbles.