CN103603042A - Ferroelectric monocrystal yttrium lead niobate-magnesium lead niobate-lead titanate as well as preparation and application thereof - Google Patents

Abstract

The invention relates to a novel ferroelectric monocrystal yttrium lead niobate-magnesium lead niobate-lead titanate and a preparation method thereof. The crystal material belongs to a perovskite type structure, wherein the chemical formula of the crystal material is (1-x-y)Pb(Y1/2Nb1/2) O[3-x]Pb(Mg1/3Nb2/3)O[3-y]PbTiO3, a PYN-PMN-PT solid solution monocrystal has a morphotropic phase boundary (MPB) region, the content x of fixed PMN is 0.44, the MPB region is located at a position in which y is equal to 0.38-0.42, the curie temperatures Tc of PYN-PMN-PT crystals are located at the MPB region and the neighborhood of the MPB region can be 125-145 DEG C, a trilateral-tetragonal phase transition temperature TRT is 90-95 DEG C, the coercive field Ec is 3-3.4 kV/cm, and the piezoelectric coefficient d33 is 1244-1608 pC/N.

Description

Ferroelectric single crystal lead yttrium niobate-lead magnesium niobate-lead titanate and its preparation and use

technical field

The invention relates to a novel ferroelectric single crystal and a preparation method thereof. Specifically, the present invention relates to a ferroelectric single crystal material (1-xy)Pb(Y _1/2 Nb _1/2 )O ₃ -x with quasi-isomorphic phase boundary (MPB) structure and relatively high Curie temperature Pb(Mg _1/3 Nb _2/3 )O ₃ -y PbTiO ₃ , abbreviated as PYN-PMN-PT, and the preparation method, structure and electrical properties of the crystal belong to the field of crystal technology and functional materials.

Background technique

Lead-based perovskite structure solid solutions, especially relaxor ferroelectric single crystal materials with lead titanate as a terminal component, are widely used in electromechanical coupling fields such as underwater acoustics, ultrasound, sensing and Micromechanical systems, especially in national defense construction, have extensive and important applications, and they are important functional ferroelectric materials that have attracted much attention. As a typical representative of relaxor ferroelectric single crystal, lead magnesium niobate-lead titanate (1-x)Pb(Mg _1/3 Nb _2/3 )O ₃ -xPbTiO ₃ (PMN-PT) has become a new generation of high Core piezoelectric materials for high-performance underwater acoustic transducers, medical ultrasonic transducers, sensors and actuators. The piezoelectric properties of PMN-PT single crystal are not only related to the Curie temperature (T _C ), but also closely related to the phase transition temperature (T _RT ) between the three parties and four parties below the Curie temperature. When the operating temperature exceeds the phase transition temperature T _RT , its piezoelectric coefficient and electromechanical coupling coefficient will decrease significantly, resulting in a great attenuation of piezoelectric performance. In addition, the coercive electric field ( _EC ) of PMN-PT single crystal is relatively low (2-3kV/cm), which limits its application in high-power ultrasonic transducers. These intrinsic defects limit the application of PMN-PT single crystal in many aspects, especially in the higher temperature range. If a new type of relaxor ferroelectric single crystal can be explored, while maintaining the excellent piezoelectric and electromechanical coupling properties of PMN-PT single crystal, the Curie temperature, trigonal-tetragonal phase transition temperature and coercive field of the material can also be improved. Strong, it can effectively make up for the intrinsic deficiency of PMN-PT single crystal, so that its electrical properties show better temperature stability, and expand the practical application range of this type of material. Therefore, exploring new high-Curie temperature and high-performance relaxor ferroelectric single crystal materials has become a key problem to be solved in the development of a new generation of ferroelectric devices.

(1-x)Pb(B′B′′)O ₃ -xPbTiO ₃ [B′: Mg ²⁺ , Zn ²⁺ , In ³⁺ , Sc ³⁺ ; B′′: Nb ⁵⁺ , Ta ²⁺ ] relaxor ferroelectric solid solution single crystal, whose end member components Pb(B′B′′)O ₃ and PbTiO ₃ belong to trigonal (pseudocubic) and tetragonal, respectively Symmetry, with the change of PT composition, there is a so-called quasi-isomorphic phase boundary (MPB) region where multiple phases coexist in the solid solution system. In this region, solid solution materials generally have good piezoelectric and electromechanical coupling properties. Since PMN-PT relaxor ferroelectric ceramics were first discovered by former Soviet scientists in 1957, people have successively discovered a series of relaxor ferroelectric ceramic systems with MPB structure, such as some binary lead-based ferroelectric materials. (1-x)Pb(In _1/2 Nb _1/2 )O ₃ -xPbTiO ₃ (PIN-PT), (1-x)Pb(Yb _1/2 Nb _1/2 )O ₃ -xPbTiO ₃ (PYN -PT), (1-x)Pb(Sc _1/2 Nb _1/2 )O ₃ -xPbTiO ₃ (PSN-PT), BiScO ₃ -PbTiO ₃ (BS-PT), etc. all have high Curie temperature , and has good piezoelectric performance and electromechanical coupling performance, which can greatly broaden the temperature and power range of the actual use of relaxor ferroelectric single crystals. Since the melting point of these binary systems is higher than that of PMN-PT, the difficulty of growth is increased. At the same time, since this type of binary system is an infinitely miscible system, direct growth of single crystals from the melt is prone to component segregation.

In contrast, ternary lead-based ferroelectric materials have the advantages of low melting point and relatively easy growth, such as lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), lead niobate-ytterbate- Lead magnesium niobate-lead titanate (PYbN-PMN-PT), lead scandate-lead magnesium niobate-lead titanate (PSN-PMN-PT), lead magnesium niobate-lead zirconate-lead titanate ( PMN-PZT), etc., its excellent piezoelectric and electromechanical coupling properties, especially the relatively high Curie temperature make this type of material is expected to become a new generation of piezoelectric materials. With the deepening of research, more and more attention has been paid to ternary ferroelectric single crystals in the field of ferroelectric materials at home and abroad, and ternary ferroelectric single crystals have become a hot spot in the field of relaxor ferroelectric materials.

Lead yttrium niobate-lead magnesium niobate-lead titanate (PYN-PMN-PT) also belongs to the composite perovskite structure, which is completely miscible in the whole composition range, and there is also a quasi-isomorphic phase boundary (MPB) region , in the quasi-isomorphic phase boundary region, showing better piezoelectric performance. Studying the preparation method, structure and electrical properties of the single crystal of the ternary system PYN-PMN-PT in the MPB region and nearby components can provide a new type of high Curie temperature and high performance for the piezoelectric field that can be used in high-power devices. ferroelectric single crystal. Contents of the invention

The purpose of the present invention is to disclose a new type of ternary ferroelectric solid solution single crystal and to study its preparation process, so as to solve the problem that the existing high Curie temperature ferroelectric single crystal is difficult to grow and there is no ferroelectric single crystal suitable for high-power devices , adding a new product for ferroelectric single crystal materials. The crystal material can be widely used in the field of piezoelectric devices.

A kind of novel ferroelectric single crystal material provided by the invention is characterized in that:

The main component compound is represented by (1-xy)Pb(Y _1/2 Nb _1/2 )O ₃ -xPb(Mg _1/3 Nb _2/3 )O ₃ -yPbTiO ₃ (PYN-PMN-PT), where , x=0.44, y=0.34～0.44, which belongs to the typical perovskite structure. The solid solution has a quasi-isotype phase boundary (MPB) region, and when x=0.44, the quasi-isotype phase region is located at y=0.38-0.42.

The preparation method of the ferroelectric crystal material of the present invention is based on the top seed crystal method capable of growing large sizes, and is characterized in that it comprises the following specific steps:

_{a) According to the chemical formula (1-xy)Pb(Y 1/2 Nb 1/2 ) O 3 -x Pb} ( _{Mg 1 / 3} Nb _2/3 )O ₃ -y PbTiO ₃ for proportioning, where x=0.44, y=0.34～0.44;

b) The flux is PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite flux, and the molar ratio of PYN-PMN-PT to flux is 1:1~10;

c) mixing and grinding the crystal raw material and the flux in a container;

d) loading the uniformly mixed powder into a platinum crucible, and placing the platinum crucible in a crystal growth furnace;

e) Heat up the crystal growth furnace until the mixed powder is in a molten state, and keep the temperature constant for a certain period of time; cool down at an appropriate cooling rate, then use the PMN-PT seed crystal to find the supersaturation temperature, introduce the seed crystal growth at the supersaturation temperature, and rotate during the growth process For seed crystals, cool down appropriately, and adjust the cooling rate according to the speed of growing crystals. When the growing crystal meets the requirements, the crystal is lifted from the melt, annealed at lower temperature, and the crystal is taken out at room temperature.

The platinum crucible used is a cylindrical crucible.

The seed crystal growth direction is (001) or (110) or (111) direction.

The crystal growth furnace adopted is a resistance heating element, and the heating element is a resistance wire or a silicon carbon rod or a silicon molybdenum rod.

The preparation methods of the crystals in the present invention all use a co-solvent, and the co-solvent is a composite co-solvent of PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ . The quality of the grown crystal is good, there is no cosolvent inclusion, and the composition uniformity is good. The crystal can be used in devices in the piezoelectric field such as sonar sensors, underwater acoustic transducers, piezoelectric igniters, capacitors, drivers, ferroelectric memories, and infrared detectors.

The ferroelectric single crystal material PYN-PMN-PT of the present invention has an MPB structure. When the PbTiO ₃ (PT) content is low, it is a trigonal perovskite structure, and when the PbTiO ₃ content is high, it transitions to a tetragonal perovskite structure. Fixed PMN content, according to the different proportions of PYN and PT, the Curie temperature Tc of the PYN-PMN-PT crystal grown in the MPB area and its vicinity can be between 125 and 145 °C, and the trigonal-tetragonal phase transition temperature T _RT is between 90～95℃, coercive field E _c (3-3.4kV/cm), piezoelectric coefficient d ₃₃ (1244-1608pC/N).

Description of drawings

Fig. 1 is the X-ray powder diffraction pattern of the PYN-PMN-PT ferroelectric single crystal prepared in Example 2 at room temperature. Powder diffractometer model: Rigaku MiniFlexП.

Fig. 2 is the dielectric thermogram of the PYN-PMN-PT single crystal prepared in Example 2 after polarization. Dielectric analyzer model: German Novolcontrol Alpha-A.

Figure 3 is the hysteresis loops of the PYN-PMN-PT single crystal prepared in Example 2 under different electric fields. The model of the ferroelectric analyzer: aix-ACCT TF2000.

Figure 4 shows the (1-xy)Pb(Y _1/2 Nb _1/2 )O ₃ -x Pb(Mg _1/3 Nb _2/3 )O ₃ -y PbTiO ₃ (PYN-PMN-PT) ternary phase picture. In the formula, x=0.44, y=0.34～0.44.

Detailed ways

The present invention will be described in further detail and complete below in conjunction with specific embodiments, but the content of the present invention will not be limited.

The crystal growth furnace that the present invention adopts is self-designed processing; The powder diffractometer (Rigaku, Japan) that is used for structural analysis adopts Rigaku diffractometer (Rigaku, Japan); The Alpha-A broadband dielectric/impedance analyzer of German Novocontrol Company is used for dielectric temperature spectrum; The hysteresis loop is measured by aix-ACCT TF2000 ferroelectric analyzer produced by Aixacct Company of Germany (frequency is 2Hz).

Example 1:

The PYN-PMN-PT ferroelectric single crystal material was grown by high temperature solution method.

The initial raw material PbO or Pb ₃ O ₄ , Y ₂ O ₃ , MgO, TiO ₂ , Nb ₂ O ₅ , the co-solvent is PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite co-solvent, according to 0.12 PYN-0.44PMN-0.44T proportional weighing, stirring, mixing and grinding. Put the uniformly mixed powder into a platinum crucible, and place the platinum crucible in a crystal growth furnace to form the material. Heat the prepared material above the supersaturation temperature, keep the temperature constant for a certain period of time, and then slowly cool down to grow; the temperature of the chemical material is between 1000-1100°C, and the temperature is lowered at a rate of 1-20°C per day; during the growth process, platinum wire can be used to hang In the center of the liquid surface, to form a nucleation center, reduce the number of nucleation and promote nucleation growth; after the growth is complete, cool down and anneal at 5-40°C/h, and then take out the crystal. Through the X-ray powder diffraction, dielectric, ferroelectric and piezoelectric performance test and analysis of the grown crystal, its structure and performance are determined.

Example 2:

The PYN-PMN-PT ferroelectric single crystal material was grown by high temperature solution method.

The initial raw material PbO or Pb ₃ O ₄ , Y ₂ O ₃ , MgO, TiO ₂ , Nb ₂ O ₅ , co-solvent using PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite co-solvent, according to the ratio 0.14PYN-0.44PMN-0.42PT weighing, stirring, mixing and grinding. Put the uniformly mixed powder into a platinum crucible, and place the platinum crucible in a crystal growth furnace to form the material. Heat the prepared material above the supersaturation temperature, keep the temperature for a certain period of time, and use the seed crystal to find the growth point to grow; grow at about 1000-1100 °C, the crystal rotation rate is 5-30 rpm, and the cooling rate is 0.1-5 °C per day; After the growth is over, the crystal is lifted out of the liquid surface, and the temperature is lowered and annealed at 5-40°C/h. The grown single crystal is a square crystal with (001) natural growth surface exposed, the crystal quality is good, there is no co-solvent inclusion, and the composition uniformity is good. Through the X-ray powder diffraction, dielectric, ferroelectric and piezoelectric performance test and analysis of the grown crystal, its structure and performance are determined.

Example 3:

The PYN-PMN-PT ferroelectric single crystal material was grown by high temperature solution method.

The initial raw material PbO or Pb ₃ O ₄ , Y ₂ O ₃ , MgO, TiO ₂ , Nb ₂ O ₅ , co-solvent using PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite co-solvent, according to the ratio 0.18PYN-0.44PMN-0.38PT weighing, stirring, mixing and grinding. Put the uniformly mixed powder into a platinum crucible, and place the platinum crucible in a crystal growth furnace to form the material. Heat the prepared material above the supersaturation temperature, keep the temperature for a certain period of time, and use the seed crystal to find the growth point to grow; grow at about 1000-1100 °C, the crystal rotation rate is 5-30 rpm, and the cooling rate is 0.1-5 °C per day; After the growth is over, the crystal is lifted out of the liquid surface, and the temperature is lowered and annealed at 5-40°C/h. The grown single crystal is a square crystal with (001) natural growth surface exposed, the crystal quality is good, there is no co-solvent inclusion, and the composition uniformity is good. Through the X-ray powder diffraction, dielectric, ferroelectric and piezoelectric performance test and analysis of the grown crystal, its structure and performance are determined.

Example 4:

The PYN-PMN-PT ferroelectric single crystal material was grown by high temperature solution method.

The initial raw material PbO or Pb ₃ O ₄ , Y ₂ O ₃ , MgO, TiO ₂ , Nb ₂ O ₅ , co-solvent using PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite co-solvent, according to the ratio 0.22PYN-0.44PMN-0.34PT weighing, stirring, mixing and grinding. Put the uniformly mixed powder into a platinum crucible, and place the platinum crucible in a crystal growth furnace to form the material. Heat the prepared material above the supersaturation temperature, keep the temperature for a certain period of time, and use the seed crystal to find the growth point to grow; grow at about 1000-1100 °C, the crystal rotation rate is 5-30 rpm, and the cooling rate is 0.1-5 °C per day; After the growth is over, the crystal is lifted out of the liquid surface, and the temperature is lowered and annealed at 5-40°C/h. The grown single crystal is a square crystal with (001) natural growth surface exposed, the crystal quality is good, there is no co-solvent inclusion, and the composition uniformity is good. Through the X-ray powder diffraction, dielectric, ferroelectric and piezoelectric performance test and analysis of the grown crystal, its structure and performance are determined.

Example 5:

The PYN-PMN-PT ferroelectric crystal materials in Examples 1, 2, 3 and 4 were subjected to structure and performance tests, and the preferred component 0.18PYN-0.44PMN-0.38PT was subjected to structure and performance tests.

a) Cut the crystal into a small piece and grind it into powder for powder diffraction. According to the powder diffraction spectrum of the obtained ferroelectric crystal, it shows that the room temperature 0.18PYN-0.44PMN-0.38PT ferroelectric crystal has a trigonal perovskite structure.

b) Cut the obtained ferroelectric crystal material into a small slice according to the (001) direction, and then smooth both sides of the slice with different sandpapers. Silver electrodes were applied on both polished and smooth sides, and polarized at 80°C under a DC electric field of 5kV/cm for 15 minutes, then kept the electric field down to room temperature, and discharged for 24 hours. The prepared samples are used for the test of piezoelectric performance d ₃₃ and dielectric thermogram. The measured piezoelectric coefficient is 1608pC/N. After measuring the piezoelectric coefficient, carry out the dielectric thermometry test, first measure the polarized sample, and then measure the depolarized sample. Measure the dielectric temperature spectrum of 0.18PYN-0.44PMN-0.38PT ferroelectric crystal, the temperature is from -50℃ to 300℃. The dielectric thermogram shows that the Curie temperature T _C of the obtained ferroelectric crystal material is 145°C; from the dielectric thermogram of the polarized sample, the trigonal-tetragonal phase transition temperature T _rt is 95°C. The dielectric constant and dielectric loss at room temperature are about 3000 and 0.023, respectively.

c) Cut the obtained ferroelectric crystal material into a small slice according to the (001) direction, and then smooth both sides of the slice with different sandpapers. Silver electrodes were applied to the polished smooth sides for the hysteresis loop test. Measure the hysteresis loops under different electric fields. Saturation is achieved under an AC electric field of +/-6kV/cm, the coercive field E _c is 3.38V/cm, and the remanent polarization P _r is 29.35μC/cm ² .

It can be seen from the above examples that the PYN-PMN-PT ferroelectric crystal material has good ferroelectric and piezoelectric properties and temperature stability, and has a promising application prospect. In addition, the above examples are only used to further illustrate the present invention, and should not be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention protected range.

Claims (9)

1. A ferroelectric single crystal material lead niobate yttrium-lead magnesium niobate-lead titanate is characterized in that: the main component compound of described formation is by (1-xy)Pb(Y _1/2 Nb _1/2 )O ₃ -x Pb(Mg _1/3 Nb _2/3 )O ₃ -y PbTiO ₃ (PYN-PMN-PT), where x=0.44, y=0.34～0.44, which belongs to typical perovskite structure. 2. The ferroelectric single crystal material according to claim 1, characterized in that there is a quasi-isomorphic phase boundary region, and when x=0.44, the quasi-isomorphic phase region is located at y=0.38-0.42. 3. a method for preparing a ferroelectric single crystal according to claim 1, comprising the steps of: _{a) According to the chemical formula (1-xy)Pb(Y 1/2 Nb 1/2 ) O 3 -x Pb} ( _{Mg 1 / 3} Nb _2/3 )O ₃ -y PbTiO ₃ for proportioning, where x=0.44, y=0.34～0.44; b) The flux is PbO or Pb ₃ O ₄ and H ₃ BO ₃ or B ₂ O ₃ composite flux, and the molar ratio of PYN-PMN-PT to flux is 1:1~10; c) mixing and grinding the crystal raw material and the flux in a container; d) loading the uniformly mixed powder into a platinum crucible, and placing the platinum crucible in a crystal growth furnace; e) Heat up the crystal growth furnace until the mixed powder is in a molten state, and keep the temperature constant for a certain period of time; cool down at an appropriate cooling rate, then use the PMN-PT seed crystal to find the supersaturation temperature, introduce the seed crystal growth at the supersaturation temperature, and rotate during the growth process For seed crystals, cool down appropriately, and adjust the cooling rate according to the speed of growing crystals. When the growing crystal meets the requirements, the crystal is lifted from the melt, annealed at lower temperature, and the crystal is taken out at room temperature. 4. The preparation method according to claim 3, characterized in that: the growth furnace is a vertical tube furnace or a box furnace, and the heating element is a resistance wire, a silicon carbide rod or a silicon molybdenum rod. 5 . The preparation method according to claim 3 , wherein the growth direction of the seed crystal during crystal growth is the (001) or (110) or (111) direction. 6. The preparation method according to claim 3, characterized in that: the temperature of the chemical material and the growth process is controlled at 850-1200°C. 7. The preparation method according to claim 3, characterized in that: the crucible used is a platinum crucible, and the shape of the crucible can be selected according to needs. 8. The preparation method according to claim 3, characterized in that: the preferred chemical composition of the recommended material is 0.18PYN-0.44PMN-0.38PT. 9. The ferroelectric single crystal material according to claim 1 is used in electromechanical transducers, exciters, capacitors, drivers, microwave communications, microwave dielectrics, filters, ultrasonic oscillators, energy harvesters and piezoelectric buzzers device field.

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