RU2736947C1 - Method of producing monophase pbin1/2ta1/2o3 indium lead tantalate with perovskite structure - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing a monophase oxide powder of composition PbIn_1/2Ta_1/2O₃ with a perovskite structure and can be used in making materials for piezo equipment, specifically for making ceramics with special properties. Method involves preparation of charge from initial oxides taken in stoichiometric ratio, at that, during charge preparation, indium and tantalum oxides are first activated, then adding averaged mixture of lead oxide and lithium carbonate, taken in amount of 1–3 wt. % of weight of stoichiometric mixture of oxides, and continuing activation, pressing of produced charge and its sintering at temperature 800–1150 °C for 1–2 hours.

EFFECT: invention provides efficient production of monophase PbIn_1/2Ta_1/2O₃ with perovskite structure, which enables to obtain bulk samples suitable for production of articles used in industry.

1 cl, 14 dwg, 1 tbl

Description

The invention relates to the field of obtaining an oxide powder of the composition Pb (In _1/2 Ta _1/2 ) O ₃ with a perovskite structure and can be used in the manufacture of materials for piezoelectric technology, namely for the manufacture of ceramics with special properties.

Piezoceramic materials are used in devices that convert mechanical effects into electrical signals and electrical signals into mechanical ones using the piezoelectric effect.

Piezoceramics is widely used in transport, energy, space and laser technology, microelectronics, and optical instruments.

The preparation of monophase perovskites is extremely important and is of great fundamental interest. These compounds are also a promising basis for the creation of ceramic capacitor, piezoelectric, pyroelectric, and posistor materials.

There are several known methods for the preparation of the perovskite monophase of the indium niobate compound PbIn _1/2 Nb _1/2 O ₃ , described in the work

(1. Paul Groves. Fabrication and characterization of ferroelectric perovskite lead indium niobate // Clarendon Laboratory, Parks Road, Oxford OX1 3PU, Great Britain. Ferroelecrrics, 1985. Vol. 65, pp. 61-77. 0015-01 93/85 /6501-0067/$20.00/0), namely:

1. Classical sintering. At the same time, samples were obtained with a perovskite phase content of 60-70% (1050 ° C and 1100 ° C and sintering for 4 hours)

2. To stabilize the perovskite structure, lithium carbonate Li ₂ CO ₃ was introduced. With the introduction of 2-10% Li ₂ CO ₃ , samples were obtained with a perovskite phase content of 80-90% (sintering for 4 hours)

3. Synthesis of perovskite through the intermediate phase of precursor synthesis

In ₂ O ₃ + Nb ₂ O ₅ = 2 (InNb0O ₎ precursor

2 (InNbO ₄ ) + 4PbO = 4 (PbIn _1/2 Nb _1/2 O3)

In this case, 1-5% In ₂ O _{3 was} added to the composition of the charge over the stoichiometric composition. In this case, samples were obtained with a maximum content of the perovskite phase> 95% (sintering for 4 hours at 950 ° C, In ₂ O ₃ 2% above the stoichiometric composition.)

According to the author, all these methods were also used to synthesize the perovskite monophase of the PbIn _1/2 Ta _1/2 O ₃ compound, however, without success. That is, it was not possible to obtain the pure phase of the monophase PbIn _1/2 Ta _1/2 O ₃ with the perovskite structure by the known methods.

A known method of producing lead indium tantalate with a perovskite structure by growing crystals from a melt.

(2. Antoni Kania. Crystallographic and dielectric properties of flux grown PbB ¹ 1/2 B ¹¹ 1 / 2O3 (B ¹ Bu ¹¹ : InNb, InTa, YbNb, YbTa and MgW) single crystals // Journal of Crystal Growth. A. Chelkowski Institute of Physics, University of Silesia, ul. Uniwersytecka 4, 40-007 Katowice, Poland. Ferroelecrics Letters, 1990, Vol. 11, pp. 107-110.)

PbIn _1/2 Ta _1/2 O ₃ single crystals were grown using the melt method. В ₂ О ₃ was introduced as a structure stabilizer. This resulted in a mixture of pyrochlore and perovskite phases. When the molar ratio of In to Ta was 1: 1, only pyrochlore crystals were obtained. The introduction of twice the amount of In ₂ O ₃ into the initial mixture allows the growth of a mixture of pyrochlore and perovskite crystals. They differ in color and shape, so they can be sorted under a microscope. Transparent, light yellow, and small (0.3 × 0.3 × 0.2 mm) cuboid crystals had a perovskite structure, like brown twin crystals. Crystals with a pyrochlore structure were dark green and in the form of a pyramid or octahedron. Pyrochlore crystals had orthorhombic symmetry. Perovskite crystals are monoclinic.

The disadvantage of this method is the impossibility of obtaining a monophasic product of lead indium tantalate with a perovskite structure. Additional sorting of crystals by phase is required. And it is completely unclear how to make a product for industrial use from these crystals, whether the perovskite structure will be preserved.

The closest technical solution, selected for the prototype, is a method of obtaining monophase PbIn _1/2 Ta _1/2 O ₃ with a perovskite structure by the method of rapid heating. The essence of this method is published in the works:

(3. Naohiko Yasuda & Susumu Imamura. Preparation and characterization of perovskite lead indium tantalate // Electrical Engineering Department, Gifu University, Gifu 501-11, Japan, Ferroelectrics, (1992), 126: 1, 109-114, DOI: 10.1080 / 00150199208227044.

4. Naohiko Yasuda, Hiroshi Inagaki and Susumu Imamura. Dielectric properties of perovskite lead indium niobate and tantalite prepared by fast firing technique // 1992 Jpn. J. Appl. Phys. 31 L574).

In these works, the InTaO ₄ compound is first sintered by calcining In ₂ O ₃ and Ta ₂ O ₅ at 1200 ° C for 24 hours, followed by pouring molten PbO to form a stoichiometric composition. Then, sintering is carried out in a rapid firing device, which consists of a tubular furnace and an external drive system, which allows the crucible with the sample to be moved into the furnace. A closed platinum crucible was installed at the end of the pusher on a platinum foil. Sintering is carried out at a temperature of 1050 ° C for 1 minute. X-ray diffraction confirms that the sample is single phase. The density of the ceramics was about 92% of the theoretical density. Sample dimensions: 0.15 mm thick and 4 mm diameter.

The disadvantage of the known technical solution is the duration of the preparation process of samples for sintering, the production of thin films of small size, the impossibility of obtaining bulk samples.

The problem solved by the claimed technical solution is to create a method for producing a monophase PbIn _1/2 Ta _1/2 O ₃ with a perovskite structure, which makes it possible to obtain bulk samples suitable for the production of products used in industry.

The problem is solved due to the fact that in the inventive method for producing monophase indium tantalate lead PbIn _1/2 Ta _1/2 O ₃ with a perovskite structure, including the preparation of a charge from initial oxides taken in a stoichiometric ratio, followed by sintering it, when preparing a charge, the initial oxides are mechanically activated. In this case, first, a mixture of indium and tantalum oxides is activated, then an average mixture of lead oxide and lithium carbonate, taken in an amount of 1-3% by weight of the weight of the stoichiometric mixture of oxides, is added to the activator, after which the second stage of activation is carried out, followed by pressing and sintering of the resulting mixture at temperature 800-1150 ° C for 1-2 hours.

The essential distinguishing features of the proposed technical solution are:

- when preparing the charge, the original oxides are subjected to mechanical activation;

- first, a mixture of indium and tantalum oxides is activated;

- then an average mixture of lead oxide and lithium carbonate, taken in an amount of 1-3% by weight of the weight of the stoichiometric mixture of oxides, is added to the activator;

- after which the second stage of activation is carried out, followed by pressing;

- sintering of the pressed samples is carried out at a temperature of 800-1150 ° C for 1-2 hours.

The set of essential distinctive features allows to solve the problem, namely, to obtain a monophase PbIn _1/2 Ta _1/2 O ₃ with a perovskite structure, which makes it possible to obtain bulk samples suitable for the production of products used in industry.

The inventive method is implemented as follows:

The initial oxides of indium, tantalum and lead, taken in a stoichiometric ratio, are subjected to mechanical activation in an AGO-2 planetary centrifugal mill in a certain sequence, namely, first, a mixture of indium and tantalum oxides is activated for 10 minutes, and then an averaged in a mortar, a mixture of lead oxide and lithium carbonate taken in an amount of 1-3% by weight based on the weight of the stoichiometric mixture of oxides and a repeated activation step is carried out. Compaction of the resulting mixture is carried out on a hydraulic press with a force of 10 t / cm ² without plasticizer. Then the obtained samples are fired at a temperature of 800-1150 ° C for 1-2 hours.

When sintering piezoceramics containing lead oxide, at high temperatures, a certain amount of lead evaporates from the surface of the samples (the lead vapor pressure increases by more than three orders of magnitude upon heating from 800 ° C to 1100 ° C). Therefore, the phase composition of the inner part of the sample and its surface is almost always somewhat different. To find out how large this difference is, the samples are ground. In addition, the specimens are also ground to the desired shape and size, as well as to apply an electrically conductive layer, such as silver, to the specimen surface.

When changing the sequence of introducing lithium carbonate into the initial oxides of indium, tantalum and lead, namely, when introducing lithium carbonate into a mixture of indium and tantalum oxides with subsequent activation for 10 minutes, adding lead oxide to the mixture and subsequent activation, samples with a reduced content are obtained. monophasic lead indium tantalate with a perovskite structure.

When synthesizing a compound from oxides without using stabilizing additives, increasing the firing time to 8 hours, as well as quenching the samples, it is possible to obtain a compound with a maximum amount of perovskite phase of 84.3% after firing for 2 hours.

When synthesizing a compound from an InTaO ₄ precursor containing the starting oxides, previously synthesized at 1100 ° C, it is possible to obtain a compound with a maximum amount of the perovskite phase of 91% after firing for 2 hours.

During the synthesis of the compound from the precursor InTaO ₄ previously synthesized at 1300 ° C, we failed to obtain samples with the perovskite structure. On the contrary, an almost monophase structure of pyrochlore was obtained.

Synthesis using hot pressing fails to obtain a single-phase product with a perovskite structure.

When the structure is stabilized with boron oxide for all variants of mechanical activation and in the entire range of firing temperatures, it is not possible to obtain a single-phase product with a perovskite structure.

It was not possible to obtain perovskite monophases with the addition of 3 wt% Li ₂ CO ₃ (after firing for one and two hours, as well as for 30 min).

Sintering at temperatures below 800 ° C does not lead to the formation of dense specimens with a perovskite structure.

Sintering at 1150 ° C leads to increased formation of the pyrochlore phase as a result of the evaporation of lead from the samples.

The implementation of the invention is illustrated by examples summarized in table No. 1 with links to the attached drawings, which show:

in fig. 1 - Diffraction patterns of samples after 10 minutes of activation and firing at a temperature of 1050 ° C and holding time for 2, 6, 8 hours. Cooling down with the oven after turning it off. The lower diffraction pattern is taken from a sample obtained by firing for 2 hours and taken out of a hot furnace (quenching);

in fig. 2 - Diffraction patterns of samples after mechanical activation for 10 minutes and firing at 1000 ° C and after mechanical activation for 25 minutes and firing at 950 ° C;

in fig. 3 - Diffraction patterns of samples after mechanical activation and firing at 600 ° C, 1000 ° C, 1300 ° C;

in fig. 4 - Diffraction patterns of samples after 25 minutes of activation and hot pressing at a temperature of 1000 ° C, a pressure of 500 kg / cm ² . The lower diffractogram is the sample after sintering, the upper diffractogram is the polished sample;

in fig. 5 - Diffraction patterns of samples containing 2% wt. In ₂ O ₃ after mechanical activation (method 1) for 10 minutes and firing for 2 hours at a temperature of 900 ° C, for 1 hour at a temperature of 900 ° C, for 1 hour at a temperature of 1150 ° C - a polished sample;

in fig. 6 - Diffraction patterns of samples of systems 1 and 2 after firing at 950 ° C;

in fig. 7 - Diffraction patterns of samples containing 1% wt. Li ₂ CO ₃ after firing for 1 hour at temperatures of 900 ° C, 900 ° C - a polished sample, 950 ° C and 950 ° C - a polished sample;

in fig. 8 - Diffraction patterns of samples containing 1% wt. Li ₂ CO ₃ after firing for 30 minutes at temperatures of 950 ° C, 950 ° C is a polished sample, 1050 ° C and 1050 ° C is a polished sample;

in fig. 9 - Diffraction patterns of samples containing 2% wt. Li ₂ CO ₃ after firing for 2 hours at temperatures of 900 ° С, 900 ° С - polished sample, 1100 ° С - polished sample and 1150 ° С - polished sample;

in fig. 10 - Diffraction patterns of samples containing 2% wt. Li ₂ CO ₃ after firing for 1 hour at temperatures of 950 ° C, 950 ° C is a polished sample, 1100 ° C and 1150 ° C is a polished sample;

in fig. 11 - Surface of samples after firing at 1000 ° C for 1 hour. 2% Li ₂ CO ₃ . Dark blotches - pyrochlore phase.

in fig. 12 - Diffraction patterns of samples containing 3% wt. Li ₂ CO ₃ after firing for 2 hours at temperatures of 1000 ° C, 1000 ° C is a polished sample and 1150 ° C is a polished sample;

in fig. 13 - Diffraction patterns of samples containing 3% wt. Li ₂ CO ₃ after firing for 1 hour at temperatures of 600 ° C, 950 ° C is a polished sample and 1000 ° C;

in fig. 14 - Diffraction patterns of samples containing 3% wt. Li ₂ CO ₃ after firing for 1 hour at temperatures of 1050 ° C (perovskite phase - 82%), 1050 ° C - polished sample (perovskite phase - 62%) and within 30 minutes 950 ° C - polished sample.

Examples of specific implementation of the method are summarized in table No. 1

As can be seen from the above examples, the inventive method allows you to solve the problem and obtain a monophasic lead indium tantalate with a perovskite structure, from which you can obtain bulk samples suitable for the manufacture of products used in industry, due to the combination of features set forth in the claims.

The appearance of the resulting monophasic lead indium tantalate is shown in Fig. eleven.

Claims (1)

A method for producing monophase lead indium tantalate PbIn _1/2 Ta _1/2 O ₃ with a perovskite structure, including preparing a charge from initial oxides taken in a stoichiometric ratio, followed by sintering it, characterized in that during the preparation of the charge, the initial oxides are mechanically activated, moreover, first, a mixture of indium and tantalum oxides is activated, then an average mixture of lead oxide and lithium carbonate, taken in an amount of 1-3 wt.% of the weight of the stoichiometric mixture of oxides, is added to the activator, after which the second stage of activation is carried out, followed by pressing and sintering of the resulting mixture at temperature 800-1150 ° C for 1-2 hours.

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