RU2534104C1 - Method of obtaining material for high temperature mass-sensitive piezoresonance sensor based on monocrystal of lanthanum-gallium alluminium tantalate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: 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 La₃Ta_0.5Ga_5.5-xAl_xO₁₄, 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.

EFFECT: increase of exploitation properties, such as the electric resistance of the material itself, increased by more than an order, and extension of the work temperature range to room temperature.

4 cl, 2 dwg, 5 tbl

Description

The invention relates to methods for growing single crystals of gallium-containing oxide compounds, namely aluminum lanthan gallium tantalate (LGTA), which has a piezoelectric effect and is used to manufacture devices on volumetric and surface acoustic waves, in particular for creating high-temperature mass-sensitive piezoresonance sensors.

Currently, the most promising material for creating high-temperature piezoelectric devices are crystals of the lanthanum gallium silicate group. The crystals of this group have thermostable acoustic sections and combine the best properties of lithium niobate crystals (high electromechanical coupling coefficient) and quartz (a number of crystal sections has a practically zero temperature coefficient of the first order frequency). In addition, phase transitions up to the melting point are absent in the crystals of the lantangallium silicate group. The lanthanum gallium silicate group could potentially include more than 350 crystals. The synthesis and research of new crystals of this group is ongoing.

Known material corresponding to the composition of La ₃ Ga ₅ SiO ₁₄ , the method of its growth by the Czochralski method includes loading pre-synthesized lantangallium silicate into a crucible, creating a protective atmosphere, then melting the material, introducing a rotating seed oriented crystal into contact with the melt surface, drawing an oriented crystal from the melt (SA Sakharov et al. Monolithic filters based on langasite crystals operating on the basic shear vibrations. - Foreign electronics M., 1986). In the known method, as LGS crystals, LGS crystals oriented along the <0001> direction are used. The crystals grown in a known manner have an orientation <0001>. (RF patent 2126064, ⁶ C30B 29/34, C30B 15/00, C01G 15/00, publ. 02/10/1999).

The disadvantage of this method is the fact that this orientation of the seed crystal does not subsequently effectively use the grown crystals to obtain LGS plates oriented with a temperature coefficient of frequency (TFC) value close to zero. In addition, the use of crystals grown in a known manner is associated with large losses of material in the manufacture of plates due to the fact that the plates are cut at a large angle from the axis of growth.

Known material adopted as a prototype for creating a high-temperature mass-sensitive piezoresonance sensor based on a single crystal La ₃ Ta _0.5 Ga _5.3 Al _0.2 O ₁₄ (LGTA), characterized by an electrical resistance of 6.01 × 10 ⁸ Ohms at T = 600 ° C (US 7947192 (B2 ), IPC C01F 17/00, С30В 15/20, publ. 2011-05-24).

A method of obtaining this material involves growing a single crystal from a melt of oxides of its constituent components in an inert gas atmosphere containing an oxidizing agent, and subsequent cooling in an inert gas atmosphere in which the molar part of the oxidizing agent is smaller than during growth. A piezoelectric sensor based on it is characterized by a working temperature range from 100 to 600 ° C.

However, the operational properties of the material, such as the electrical resistance of the material itself and the operating temperature range of devices based on it, are insufficient for the current level of technology.

The present invention solves the problem of obtaining material for piezoelectric sensors with enhanced operational properties.

The problem is solved by the method of obtaining material for a high-temperature mass-sensitive piezoresonance sensor based on a single crystal of aluminum lantangallium tantalate, the composition of which corresponds to the formula La ₃ Ta _0.5 Ga _5.5-x Al _x O ₁₄ , where x = 0.1-0.3, characterized by an electrical resistance not less than 10 ⁹ Ohms at a temperature of 20-600 ° C, including the growth of a single crystal from a melt of oxides of its constituent components in an inert gas atmosphere containing an oxidizing agent, the novelty of which is that the resulting single crystals from the melt are further annealed in air at a temperature of 1050–1150 ° C for 41–43 hours.

The best results are obtained when annealing in air at a temperature of 1100 ° C for 42 hours.

After annealing, the single crystals are cut into billets and subjected to their second additional annealing in vacuum at a temperature of 1150-1250 ° C for 9-11 hours.

The best results are obtained by annealing the workpieces in vacuum at a temperature of 1200 ° C for 10 hours.

The technical result is to increase operational properties, such as the electrical resistance of the material itself, increased by more than an order of magnitude, and the expansion of the operating temperature range to room temperature.

Table 1 shows the results of solid-phase conversion in LGTA, where * O = monophasic, X = contains extraneous phases

Table 2 shows the results of a phase analysis of LGTA crystals with different molar concentrations of aluminum in the composition of the crystal.

Table 3 shows the values of the electrical resistance of the crystal at a temperature of T = 600 ° C depending on the time and temperature of annealing.

Table 4 shows the electrical resistance values of single-crystal LGTA plates at a temperature of T = 600 ° C depending on the time and temperature of the second additional annealing.

Table 5 summarizes the main characteristics of a high-temperature, low-sensitivity piezoresonance sensor for microbalances made on the basis of a single crystal LGTA.

Figure 1 shows a high-temperature mass-sensitive piezoresonance sensor for microbalances.

Figure 2 shows the design of a high-temperature, low-sensitivity piezoresonance sensor for microbalances.

The following examples confirm, but do not limit, the invention.

Example 1

To obtain the initial mixture for the synthesis of single crystals of aluminum lanthan gallium tantalate, gallium oxide Ga ₂ O _3, tantalum pentoxide Ta ₂ O ₅ , and aluminum oxide Al ₂ O _{3 were used} . The starting components were qualified as HSP.

The initial charge for growing LGTA crystals was obtained by solid-phase synthesis. Weighed portions were taken from previously calcined starting components in accordance with the stoichiometric composition according to the formula of the compound La ₃ Ta _0.5 Ga _5.5-x Al _x O ₁₄ (x = 0.1, 0.3, 0.4, 0.6). The homogenization of the initial mixture was carried out in installations of a vibro-boiling layer for 4 hours. The briquettes were pressed using molds made of plexiglas at a pressure of up to 2.5 atm. The mixture was synthesized in a high-temperature furnace at a temperature of 1200 ° C for 8 hours. The completeness of the process was monitored by x-ray phase analysis. The study of the resulting mixture by x-ray phase analysis showed the presence of the main phase of LGA not less than 95% of the initial mass.

LGTA crystals were grown by the Czochralski method with an induction method for heating the crucible. Iridium was selected as the crucible material. Argon was used as an inert gas in the atmosphere of which single crystals were grown. Oxygen was used as an oxidizing agent, the content of which in the mixture was 0.5 volume percent. The seed crystals were oriented along the crystallographic axis [11.0]. The rate of drawing the crystal from the melt was 0.5 mm / h at a rotational speed of 11 rpm. Table 1 shows the results of solid-phase conversion in LGTA. The results of the phase analysis are presented in table 2.

A crystal grown with an aluminum content in the initial charge of 0.4 f.e. and more, shows the presence of the perovskite phase of La (Ga, Al) O ₃ .

Thus, it was found that in order to obtain a monophasic LGTA crystal, the molar concentration of aluminum should correspond to x = 0.1-0.3.

After the growth process, LGA crystals were subjected to high-temperature annealing in air at a temperature of 1050–1150 ° С for 41–43 hours. Annealing of LGTA crystals in air led to a change in the color of the crystals from weak pink to light yellow.

Table 3 shows the values of the electrical resistance of the crystal of electrical resistance (Ohms) of the LGTA single crystal at a temperature of T = 600 ° C depending on the time and temperature of the annealing. As can be seen from the table, only annealing in the claimed intervals of temperature and time allows to achieve the claimed characteristics of a single crystal. Reducing the annealing time of less than 41 hours, as well as conducting it at an annealing temperature below 1050 ° C, leads to a decrease of no less than an order of electrical resistance of the obtained single crystals. Increasing the annealing time of more than 43 hours and conducting it at temperatures above 1150 ° C are not economically feasible, since they do not affect the final result with an increase in energy consumption.

Example 2

All operations are carried out in accordance with example 1. The difference is that after annealing in air and cutting a single crystal of LGTA into billets, the billets are subjected to additional annealing in vacuum at a temperature of 1150-1250 ° C for 9-11 hours. An additional vacuum annealing procedure leads to the disappearance of color centers, as well as to an increase in the electrical resistance of single-crystal plates. The test results are shown in table 4.

Example 3

Based on the LGTA single crystal, a high-temperature mass-sensitive piezoresonance sensor for microbalances was developed (Fig. 1). The design of the sensor is shown in figure 2. In the manufacture of the sensor for the formation of electrodes, iridium I99.8 STO 72386442-029-2009 was used. A 100 nm thick iridium layer was deposited through the mask by magnetron sputtering.

Table 5 shows the main characteristics of the sensor, confirming the achievement of the maximum combination of currently known values characterizing the operation of similar sensors.

As can be seen from the above examples, the patented material has an electrical resistance that is an order of magnitude higher than the electrical resistance of the prototype, and piezoelectric devices based on this material are operable in the temperature range from room temperature to 600 ° C, which is an extension of the working temperature range of the prototype (100- 600 ° C).

Table 1 MATERIAL FOR CREATION OF A HIGH-TEMPERATURE MASS-SENSITIVE PIEZORESONANCE SENSOR BASED ON A MONOCRYSTAL OF LANTANGALLIUM ALUMINUM TANTSALATE, METHOD FOR ITS PREPARATION The composition of the starting mixture La ₃ Ta _0.5 Ga _5.5-x Al _x O ₁₄ Solid Phase Reaction Results * La ₃ Ta _0.5 Ga _5.4 Al _0.1 O ₁₄ (x = 0.1) O La ₃ Ta _0.5 Ga _5.2 Al _0.3 O ₁₄ (X = 0.3) O La ₃ Ta _0.5 Ga _5.1 Al _0.4 O ₁₄ (x = 0.4) X La ₃ Ta _0.5 Ga _4.9 Al _0.6 O ₁₄ (x = 0.6) X

table 2 MATERIAL FOR CREATING A HIGH-TEMPERATURE MASS-SENSITIVE PIEZORESONESANCE SENSOR BASED ON A SINGLE CRYSTAL OF AN ALUMINUM TANTALATE, A METHOD FOR ITS PREPARATION AND A SHIELD SHARPENER Composition Lattice constants Phase results La ₃ Ta _0.5 Ga _5.5-x Al _x O ₁₄ a (Å) s (Å) La ₃ Ta _0.5 Ga _5.4 Al _0.1 O ₁₄ 2009.2009 LTGA (x = 0.1) 5.1049 La ₃ Ta _0.5 Ga _5.2 Al _0.3 O ₁₄ 8.1982 LTGA (x = 0.3) 5.0943 La ₃ Ta _0.5 Ga _4.9 Al _0.6 O ₁₄ 8.1980 LTGA + La (Ga, Al) O ₃ (x = 0.4) 5.0939

Table 5 MATERIAL FOR CREATING A HIGH-TEMPERATURE MASS-SENSITIVE PIEZORESONANCE SENSOR BASED ON A SINGLE CRYSTAL OF ALTANGALLIUM ALUMINUM TANTALATE, METHOD FOR ITS PREPARATION AND HIGH-RESISTANCE RESPONSE Resonance frequency, MHz eleven Resonance frequency tuning accuracy -8 · 10 ^-6 -9 · 10 ^-6 The accuracy of maintaining the extreme point, ° C ± 0.6 Operating temperature range, ° С 20-600 Range of measurements, g 3 · 10 ^-8 -6 · 10 ^-4 Sensitivity, MHz / mg 1.60-1.67 Resolution, g ^10-11

Claims (4)

1. A method of obtaining a material for a high-temperature mass-sensitive piezoresonance sensor based on a single crystal of aluminum lantangallium tantalate, the composition of which corresponds to the formula La ₃ Ta _0.5 Ga _5.5-x Al _x O ₁₄ , where x = 0.1-0.3, characterized electrical resistance of at least 10 ⁹ Ohm at a temperature of 20-600 ° C, comprising growing a single crystal from a melt of its components oxides under an inert gas atmosphere containing an oxidizing agent, characterized in that the single crystals obtained from the melt additionally annealing in the air at a temperature of 1050-1150 ° C for 41-43 hours. 2. The method according to claim 1, characterized in that the annealing in air is carried out at a temperature of 1100 ° C for 42 hours. 3. The method according to claim 1, characterized in that after annealing, the single crystals are cut into preforms and subjected to their second additional annealing in vacuum at a temperature of 1150-1250 ° C for 9-11 hours. 4. The method according to claim 3, characterized in that the second additional annealing in vacuum is carried out at a temperature of 1200 ° C for 10 hours.

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