Method for formation of bidomain structure in single-crystal plates

FIELD: construction.

SUBSTANCE: 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.

EFFECT: invention makes it possible to change from traditionally used piezoceramic elements of deformation to single-crystal bidomain elements of precise positioning on the basis of single crystals of ferroelectrics with high Curie temperature, which do not have creep and hysteresis.

2 cl, 2 dwg, 1 ex

 

The invention relates to a method of forming the single crystal ferroelectrics balomenou patterns for use in the devices of nano-and micromechanics, where there is a need to maintain accurate, repeatable and without permanent deformation, the mechanical movement in the micro - and nondiapausing. This applies both to the measuring technique, in particular, a probe microscope, and functional devices manufactured by MEMS technology.

The main constructive element of such devices any modification is an Electromechanical device that converts electrical energy in a controlled motion i.e. microactuator. Perspective methods of activation should include piezoelectric bimorph elements based bigemeny structures in single crystal ferroelectrics. However, at present there are no reliable methods of forming the bimorph domain structure in ferroelectric crystals

There are several different ways of forming crystals of the ferroelectric system domains of a given size and orientation of cross-borders [Periodically polarized domain structure due to the use of the system of electrodes. FTT. 1999 v.41 s-1837. Shur WA, E. Rumyantsev, Bacco RG and others; Surfase domain engineering in congment lithum niobate single crystals. Applied physics letters, v.81, N26, 4946-4948, 2002. A.C. Busacca, C.L. Sones, V. Apostolopoulos, R.W. Eason and S. Mailis.]. Crystals, polarized in these methods are polydomain, i.e. contain the volume of the ferroelectric domains are oriented antiparallel. However, for manufacturing a bimorph structures such domain of education are not suitable since it is necessary that the two faces of the crystal which is applied to the control electrodes were cut parallel to the domain wall and had a large enough area to obtain the necessary mechanical energy when the elastic deformation of the bimorph. The proposed methods cannot polarize crystals with a thickness of more than 0.2-0.5 mm and an area of more than a few square millimeters. In addition, their geometry does not allow you to use the maximum piezoelectric modules.

The closest analogue to the proposed method is a method of producing single crystals of lithium niobate with balomenou structure by applying electrodes on the two faces of a crystal when heated to the phase transition temperature is the Curie temperature under the action of a nonuniform electric field [ANTIPOV CENTURIES and others, the Formation of balomenou patterns in the wafer of single crystal lithium niobate electro-thermal method, "Izv. Ser. Materials of electronic engineering", 2008, №3, p.18-22].

The disadvantages of the known ability, the BA is the inability to create a plane-parallel domain structure in single crystals of lithium niobate and the lack of specific data, under which achieves this structure.

The technical result of the claimed invention is to obtain single crystals of lithium niobate with balomenou structure having a flat cross-border, and maximum deformation.

The technical result of the invention is achieved by a method of producing single crystals of lithium niobate with balomenou structure for devices of nano-and micromechanics by applying electrodes in the form of a system of parallel strings of two plane-parallel faces of the crystal, oriented at an angle z+36° to the polar axis, when heated to the phase transition temperature is the Curie temperature under the action of a nonuniform electric field. The electrodes may be made of palladium paste and applied on sapphire wafers.

When applying a DC electric potential to the electrodes in the form of a system of parallel strings creates a non-uniform electric field with a given spatial distribution of the magnitude and direction of the field lines in the crystal. The polarization of the ferroelectric is due to the fact that when the temperature of the phase transition metal ions, for example, lithium niobate, have high mobility, conductive to the fact that under the influence of an electric field the ions in crystalline cationic sublattice who are moved, and after lowering the temperature condition is fixed. The direction of bias depends on the power lines of the electric field determines the direction of the polarization vectors in the crystal.

The angle of orientation of the faces of the crystals relative to the polar axis is selected as the maximum piezomodulus used for ferroelectric crystal at the stage of manufacturing blanks for the formation of bimorph structures. This allows you to get maximum mechanical deformation of a compression-tension" when the application of electric fields.

The resulting projection of the electric field intensity vector of the same charge electrodes varies along the thickness of the crystal, the electric field maximum in the polar faces, and close to zero in the middle of the crystal, where the plane of zero potential. The electrodes provide the ability to control the position of a domain wall, its shape and volume of domains of different polarization.

To obtain structures with a single domain boundary in the plate of lithium niobate used a system of electrodes, creating heterogeneous, symmetric with respect to the boundaries of the electric field in the crystal volume. When the cooling plate from the Curie temperature is sprouting two domains with opposite directions of the field vectors is Itachi from electrodes deep into the crystal. Direction and speed are set by the density distribution and orientation of the lines of force of the electric field in the plate. It is necessary to ensure the emergence and germination of domains over the entire area of the crystal. Domains found in the region of zero potential and an electric field is formed in the crystal bidomain with one border in the middle.

Crystal with electrodes placed in a furnace, which provides heating to the Curie temperature for this material, the necessary exposure of the crystal under the field that provides the formation and germination of domains into the volume of the crystal, and then decrease slowly to room temperature. Germination occurs from the edges of the crystal in opposite directions into the crystal. After cooling the ferroelectric crystal has two mono-domain region of equal volume with the opposite direction of the polarization vectors of the flat cross-border. Such specified spatial distribution over the crystal volume of the polarization vector forms balomenou structure.

The proposed method allows to control the position and topology of boundaries, to change the intensity and configuration of the electric field.

An example of carrying out the process of forming a bimorph structure in the single crystal of lithium niobate.

Between the two of SAPF the world plates (1) was placed ferroelectric crystal of lithium niobate LiNbO 3given geometrical dimensions (2) with plane-parallel faces. The perpendiculars to these edges do not coincide with the direction of the axis of spontaneous polarization of the crystal and are selected from the condition of maximum piezomodulus for the selected ferroelectric at the stage of manufacture plates. To create a nonuniform electric field on the crystal volume PA both sapphire plate was deposited metal electrode (3) in the form of a system of parallel scab. The electric field inside the electrodes is the sum of the intensities of the electric fields generated by each electrode. The width of the electrodes, their age and thickness depend on the geometry of the crystal and placed in the production process.

On the basis of computer models calculate the distribution of electric field intensity on the thickness of the crystal of the ferroelectric, theoretical distribution of polarization depending on various conditions of the process of forming balomenou patterns. The calculation takes into account the width of the electrodes and the distance between them, the number of electrodes, the distance between the electrodes applied to the electrode potential, the mixture relative to each other of the electrodes and the inaccuracy of determining the crystallographic orientation of the crystal, the installation process cell.

The voltage vector is nasty electric field varies along the thickness of the crystal and the maximum field strength on the faces of the crystal and drops to zero in the bulk of the crystal. On the geometry and position of the cross-border impact the following technical characteristics: the distance between the strings of the electrodes, the distance between the electrodes and the crystal inaccuracies in the Assembly work cell during the formation of the bimorph - overlapping with each other without shifting of electrode plates, the combination of the polarization direction and the electrodes.

Inaccuracies orientation and alignment of the electrodes can lead to distortion of the flat shaped cross-border, her twisting and deterioration of performance characteristics of the bimorph.

For the manufacture of electrodes on a round plate made of synthetic sapphire diameter of 76 mm and 0.5 mm thick layer of liquid palladium paste, then plate parts are annealed at 700°C to remove the organic solvent of the paste. The electrode structure is created by pulsed laser radiation of the second harmonic garnet laser with a wavelength of 532 nm with an energy of 80 MJ, which removes part of the conductive palladium coatings by evaporation focused 10 pulses. The width of the obtained electrodes is 0.22 mm and the distance between them - 0.85 mm were selected from the calculations according to the described method taking into account the geometry of the crystal and the distance between him and the electrodes (figure 1).

The sample in the form of a rectangular plate monocrystal is as lithium niobate with dimensions of 40 mm (slice Z+36°) 20 mm (slice X) and a thickness of 1.5 mm (with faces perpendicular to the crystallographic Y direction - 127,86°) (2), is placed between the plates with conductive palladievye electrodes on sapphire (1, 3), so that the strings of the electrodes were spatially coincident, and the X direction was perpendicular to the strings (figure 2). The electrodes are connected wire platinum contacts (4)electrically connecting both plates with electrodes, and then collected the working cell is placed in a gradient oven.

Bake evenly heated to the phase transition temperature of congruent lithium niobate composition - 1150°C for (3-3,5 hours, direct voltage 1000 B to the electrodes, the crystal is aged for 30 minutes and then under a constant electric field begins a slow cooling furnace to 800-850°C for 60 minutes. Electric field and heat are turned off when the temperature drops to the temperature that provides the origin of the domains on the flat faces of the crystal, the germination of domain boundaries on the volume of the crystal and the formation of a single domain wall in the middle of the plate. Full inertial cooling the furnace to room temperature lasts 12-14 hours. The depth of germination of domain boundaries depends primarily on the exposure time of the crystal below.

Studies of morphology and visualization of the obtained domain structure in lithium niobate crystal by x-ray diffractometer and and atomic force microscopy confirmed that under the influence of an inhomogeneous electric field annealing is strongly bigemina structure.

The efficient and stable conversion of an electrical signal in Flexural mechanical elastic deformation on the experimental layout with a cross section of the domain bimorph element 2×8×1 mm at the console consolidation is characterized by the following characteristics: change of deformation in voltage ranges from 20 to 500 V/mm is 0.04 to 0.5 μm, the residual deformation of the elements is not more than 0.3%, the linearity of the deformation is not worse than 1% in the temperature range from room temperature to 850°C.

From the test results we can conclude that the longitudinal-Flexural deformation obtained bimorph crystal structures are characterized by the absence of mechanical hysteresis, creep and permanent deformation in a wide range of operating temperatures with high linearity values of deformation bimorphs from the electric signal.

1. A method of producing single crystals of lithium niobate with balomenou structure for devices of nano-and micromechanics by applying electrodes on the two faces of a crystal when heated to the phase transition temperature is the Curie temperature under the action of a nonuniform electric field, characterized in that the crystal face is parallel-sided, Crist is ll oriented at an angle z+36° to the polar axis, as the electrodes are designed in the form of a system of parallel strings.

2. The method according to claim 1, characterized in that the electrodes are made of palladium paste and applied on sapphire wafers.



 

Same patents:

FIELD: chemistry.

SUBSTANCE: 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.

EFFECT: invention enables to form a charged domain wall, having an irregular three-dimensional shape with given geometric parameters, lying at a given depth in a monocrystalline ferroelectric plate without heating the plate or cutting a workpiece for making the plate.

4 cl, 7 dwg

FIELD: process engineering.

SUBSTANCE: invention relates to processes used in operation at high pressure and modifying substances physically. Proposed method comprises placing diamond in reaction cell in pressure transmitting medium, increasing pressure in reaction chamber and it cooling. Note here that thermal treatment is carried out at temperature increase rate of 10-50°C/s and at 2000-2350°C by passing electric current via heater in cell from programmed power supply source with due allowance for temperature relaxation in said cell in heating. For this, note also that temperature relaxation constant is defined. Said cell is cooled after heating by switching off power supply in forming short diamond heating pulse in temperature range of over 2000°C with diamond total stay time smaller than 30 seconds. Allowance for temperature relaxation in said cell in heating for heating rate Vt and pre-definition of cell temperature relaxation constant τ is made by setting in said programmable power source the maximum temperature of heating to τVT above maximum treatment temperature of 2000-2350°C.

EFFECT: changing colour of low-grate natural diamond without notable graphitisation, high-quality gem diamonds.

2 cl, 5 dwg, 3 ex

FIELD: physics.

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EFFECT: image from a cluster of N-V centres is inside the crystal, cannot be removed by polishing and is therefore a reliable diamond signature and reliable recording of information without destroying or damaging the crystal itself.

46 cl, 3 dwg

FIELD: chemistry.

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FIELD: chemistry.

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EFFECT: invention increases the effectiveness of the process of cleaning diamonds larger than 4,0 mm with high efficiency of the equipment used.

3 cl, 3 dwg, 2 tbl, 1 ex

FIELD: metallurgy.

SUBSTANCE: procedure consists in ion-energy-beam processing diamonds with high power ion beam of inert chemical element of helium with dose of radiation within range from 0.2×1016 to 2.0×1017 ion/cm2 eliminating successive thermal annealing.

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FIELD: metallurgy.

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5 cl, 1 tbl

FIELD: physics.

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EFFECT: invention increases the possible volume of irradiated specimens and increases efficiency of modifying minerals.

1 dwg

FIELD: metallurgy.

SUBSTANCE: 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.

EFFECT: method provides increasing of efficiency of monocrystals polarising of lithium tantalate, different by orientation, dimensions and conditions of growing; shaped interlayer provides durable and uniform cohesion of crystal surface to electrodes, and current and voltage stabilisation and fixed rate of crystal cooling in the range of temperature Curie provide guaranteed receiving of transparent, blast-furnace crystals of lithium tantalite without additional defects in the form of cracks and disruptions.

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2 ex, 1 tbl

FIELD: chemistry.

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2 ex

FIELD: chemistry.

SUBSTANCE: fluoride nanoceramic is obtained by thermomechanical treatment of the starting crystalline material made from CaF2-YbF3, at plastic deformation temperature to obtain a workpiece in form of a polycrystalline microstructured substance, which is characterised by crystal grain size of 3-100 mcm and a nanostructure inside the grains, by annealing on air at temperature of not less than 0.5 of the melting point with compaction of the obtained workpiece in a vacuum at pressure of 1-3 tf/cm2 until the end of the deformation process, followed by annealing in an active medium of carbon tetrafluoride at pressure of 800-1200 mmHg. The starting crystalline material used can be a fine powder which has been subjected to heat treatment in carbon tetrafluoride, or a moulded workpiece of crystalline material made from the powder and heat treated in carbon tetrafluoride.

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4 cl, 3 ex

FIELD: process engineering.

SUBSTANCE: invention relates to processes used in operation at high pressure and modifying substances physically. Proposed method comprises placing diamond in reaction cell in pressure transmitting medium, increasing pressure in reaction chamber and it cooling. Note here that thermal treatment is carried out at temperature increase rate of 10-50°C/s and at 2000-2350°C by passing electric current via heater in cell from programmed power supply source with due allowance for temperature relaxation in said cell in heating. For this, note also that temperature relaxation constant is defined. Said cell is cooled after heating by switching off power supply in forming short diamond heating pulse in temperature range of over 2000°C with diamond total stay time smaller than 30 seconds. Allowance for temperature relaxation in said cell in heating for heating rate Vt and pre-definition of cell temperature relaxation constant τ is made by setting in said programmable power source the maximum temperature of heating to τVT above maximum treatment temperature of 2000-2350°C.

EFFECT: changing colour of low-grate natural diamond without notable graphitisation, high-quality gem diamonds.

2 cl, 5 dwg, 3 ex

FIELD: process engineering.

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EFFECT: higher quality.

1 cl

FIELD: process engineering.

SUBSTANCE: invention relates to diamond processing, in particular, by thermochemical process. Proposed method comprises applying layer of spirit glue composition onto diamond surface, said composition containing transition metal, for example, Fe, Ni or Co, and processing diamond thermally at temperature not exceeding 1000°C. To prepare spirit glue composition, powder of water-soluble salt of transition metal is used. Said powder in amount of 1-10 wt % of water solution is mixed with spirit solution of glue at salt water solution-to-glue spirit solution ratio of 1:1. Prepared mix is applied on diamond surface in 10-20 mcm-thick layer to be dried. Thermal processing of diamond is performed in two steps. Note here that, at first step, diamond is processed at 600-700°C for 1-2 min, while, at second step, it is processed at 800-1000°C for 15-30 min.

EFFECT: superhigh specific surface with nano-sized (100-200 nm) relief, expanded applications.

2 dwg, 7 ex

FIELD: physics.

SUBSTANCE: method involves thermomechanical processing of initial crystalline material made from metal halides at plastic deformation temperature, obtaining a polycrystalline microstructured substance characterised by crystal grain size of 3-100 mcm and intra-grain nanostructure, where thermomechanical processing of the initial crystalline material is carried out in vacuum of 10-4 mm Hg, thus achieving degree of deformation of the initial crystalline material by a value ranging from 150 to 1000%, which results in obtaining polycrystalline nanostructured material which is packed at pressure 1-3 tf/cm2 until achieving theoretical density, followed by annealing in an active medium of a fluorinating gas. The problem of obtaining material of high optical quality for a wide range of compounds: fluoride ceramic based on fluorides of alkali, alkali-earth and rare-earth elements, characterised by a nanostructure, is solved owing to optimum selection of process parameters for producing a nanoceramic, which involves thermal treatment of the product under conditions which enable to increase purity of the medium and, as a result, achieve high optical parameters for laser material.

EFFECT: nanosize structure of the ceramic and improved optical, laser and generation characteristics.

3 cl, 3 ex

FIELD: machine building.

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4 cl, 1 dwg

FIELD: physics.

SUBSTANCE: method involves subjecting a grown and hardened, i.e. correctly annealed crystal, to secondary annealing which is performed by putting the crystal into a graphite mould, the inner volume of which is larger than the crystal on diameter and height, and the space formed between the inner surface of the graphite mould and the surface of the crystal is filled with prepared crumbs of the same material as the crystal. The graphite mould is put into an annealing apparatus which is evacuated to pressure not higher than 5·10-6 mm Hg and CF4 gas is then fed into its working space until achieving pressure of 600-780 mm Hg. The annealing apparatus is then heated in phases while regulating temperature rise in the range from room temperature to 600°C, preferably at a rate of 10-20°C/h, from 600 to 900°C preferably at a rate of 5-15°C/h, in the range from 900 to 1200°C preferably at a rate of 15-30°C/h, and then raised at a rate of 30-40°C/h to maximum annealing temperature depending on the specific type of the metal fluoride crystal which is kept 50-300°C lower than the melting point of the material when growing a specific crystal, after which the crystal is kept for 15-30 hours while slowly cooling to 100°C via step-by-step regulation of temperature decrease, followed by inertial cooling to room temperature.

EFFECT: high quality of producing monocrystals of metal fluorides owing to increase in their homogeneity with maximum reduction of defects in grown crystals, which ensures high yield of the material with good optical characteristics, use of a special mode of preparation and carrying out secondary annealing primary grown and hardened crystals of metal fluorides enable to eliminate microinhomogeneities and small-angle off-orientations of crystals.

1 ex

FIELD: electricity.

SUBSTANCE: method includes the first stage of increasing temperature of single-crystal substrate ZnTe up to the first temperature of thermal treatment T1 and maintenance of substrate temperature within specified time; and the second stage of gradual reduction of substrate temperature from the first temperature of thermal treatment T1 down to the second temperature of thermal treatment T2, lower than T1 with specified speed, in which T1 is established in the range of 700°C≤T1≤1250°C, T2 - in the range of T2≤T1-50, and the first and second stages are carried out in atmosphere of Zn, at the pressure of at least 1 kPa or more, at least 20 cycles or at least 108 hours.

EFFECT: invention makes it possible efficiently to eliminate part of Te deposits without considerable deterioration of efficiency and improvement of light transmission of single-crystal substrate ZnTe.

5 cl, 3 dwg

FIELD: chemistry.

SUBSTANCE: crystals are grown using the Kyropoulos method with an optimum annealing mode, carried out while lowering temperature of the grown monocrystal to 1200°C at a rate of 10-15°C/hour and then cooling to room temperature at a rate of 60°C/hour.

EFFECT: obtaining large monocrystals with less stress in the entire volume, and which are suitable for mechanical processing in order to obtain crystal wafers with zero orientation.

1 ex, 1 dwg

FIELD: chemistry.

SUBSTANCE: 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.

EFFECT: invention enables to form a charged domain wall, having an irregular three-dimensional shape with given geometric parameters, lying at a given depth in a monocrystalline ferroelectric plate without heating the plate or cutting a workpiece for making the plate.

4 cl, 7 dwg

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