Fig. 1 is the sectional view of crystal growing furnace.1 is Heating element (SiC or MoSi among the figure
2Rod), 2 is platinum crucible, and 3 is refractory materials (Al
2O
3) crucible, 4 is Al
2O
3Packing material (the Al of crucible
2O
3Powder), 5 is refractory materials (Al
2O
3Brick), 6 are following descending mechanism.
Fig. 2 .PMNT crystal growing furnace is along the warm curve of field distribution of the direction of growth.Among the figure X-coordinate be temperature (℃), ordinate zou be the height (cm), I is the high-temperature zone, II is a temperature gradient zone, III is a cold zone,---be desirable temperature curvature of field line, ◆ be reality temperature curvature of field line
Fig. 3. be the large size PMNT single crystal that preparation method provided by the invention grew.
Fig. 4,5 is respectively the relation between specific inductivity (ε), loss (tan δ) and the temperature (T) of 0.76PMN-0.24PT monocrystalline and 0.67PMN-0.33PT monocrystalline.X-coordinate be temperature (℃), left side ordinate zou is represented specific inductivity, right side ordinate zou is represented dielectric loss.The test frequency shown in a, b, c, the d is respectively 100Hz, 1kHz, 10kHz and 100kHz among the figure
Fig. 6 is that the electricity of 0.67PMN-0.33PT monocrystalline is led the relation curve between G, resistance R and the frequency f.X-coordinate is frequency (Hz), and left ordinate zou is that electricity is led (I/ Ω), and right ordinate zou is resistance R (Ω).
Fig. 7 is under the different frequency, the relation between the specific inductivity of 0.65PMN-0.35PT monocrystalline (ε), loss (tan δ) and the temperature T.X-coordinate be temperature (℃), left side ordinate zou is represented specific inductivity (ε * 10
-3), right side ordinate zou is represented dielectric loss (tan δ).
Further specify the present invention in conjunction with preferred embodiment with reference to the accompanying drawings.
(1) raw material is handled
Handling about raw material, mainly is to determine the accurate afterwards various oxide raw materials of weighing of x value according to xPMN-(1-x) PT chemical formula.
Described raw material is handled and is comprised batching, and mixed, static pressure becomes piece and calcining.To the material purity general requirement more than 3N, more than the preferred 4N, as long as can grow adaptable monocrystalline.Raw material can static pressure also not static pressure become piece, if without static pressure, general melt repeatedly then is so preferably use static pressure.Do not have a strict restriction to mixed, general mixed apparatus all can use, as long as the raw material that makes preparation evenly, preferably mixes on ball mill.With purity greater than 99.99% PbO, Pb
3O
4, MgO, Nb
2O
5, TiO
2Powder be made into mixing raw material, x=0.60~0.80 by xPMN-(I-x) PT chemical formula; Then based on the raw material total amount add a certain amount of PbO as solubility promoter, its mol ratio is 100xPMN-(1-x) PT: 0~10PbO, to reduce the temperature of fusion of mixed powder; Again with joining the raw material ball milling be mixed into uniform powder in 1~10 hour, expect as rising of crystal growth through hydrostaticpressure or compression molding.
Crucible is not had strict restriction equally, as long as can bear growth temperature simultaneously not with raw material reaction, for example metal or alloy crucible, particularly precious metal crucible, the oxide compound crucible of coating, nitride crucible or the like.Wherein preferred simple platinum crucible.In order to prevent the volatilization of PbO, after installing the platinum crucible welded seal of seed crystal and growth raw material, carry out crystal growth.
The thickness of crucible and shape all do not have strict restriction, and thickness is got over Bao Yuehao under the prerequisite that can bear melt, so that reduce cost as much as possible.The quantity of crucible and shape do not have strict restriction equally, for reducing cost the particularly special-shaped crucible of the many crucibles of a preferred stove, that is the special-shaped crucible of crystal shape that the user requires.This respect Shanghai silicate a plurality of patents open, CN1113970A for example, this paper is in conjunction with reference for its content.The diameter of platinum crucible is changeable among the present invention, be generally 10~50mm, the length of crucible also without limits, be generally 200~400mm, and can be according to needed PMNT crystalline shape, platinum crucible is made into corresponding shape, and platinum crucible can be that (every layer thickness is preferred 0.10~0.20mm), with corrosion and the volatilization that prevents PbO for the individual layer of sealing or bilayer structure.
From the crystal growth principle, use the polycrystal raw material growth more favourable, this is well known in the art.Therefore in another embodiment, above-mentioned powder of joining is put into platinum crucible, be that solid state sintering becomes the PMNT material of perovskite structure and the compound of PbO under 1100~1260 ℃ the condition in temperature, then sintered material is ground thorough mixing, expect as rising of crystal growth through hydrostaticpressure or compression molding again.
Or in another embodiment the moulding of raw material binder is joined by above-mentioned institute, and to put into platinum crucible then and be under 1290~1400 ℃ the condition after the fusing in temperature, casting is cooled to polycrystal, as expecting of crystal growth.
(2) growth technique and crystal growing furnace
The difficulty of Bridgman-Stockbarge method for growing PMNT is to determine suitable growth technique condition, comprise the warm field distribution of determining growth furnace, the thermograde of solid-liquid interface, the speed that crucible descends, and along with the decline of crucible, the timely adjusting of temperature field avoids producing burnt green stone phase to reach in the stove, guarantees to grow the uniform PMNT monocrystalline of component.
During the PMNT single crystal growing, can use or not use seed crystal.If the use seed crystal, the PMNT monocrystalline that can select not have bulk defects is made seed crystal.The seed crystal direction does not have strict restriction, can decide according to user's needs.Be generally<001,<110 or<111, can determine that at normal temperatures the crystallographic direction of PMNT monocrystalline is as the seed crystal direction with commercially available monocrystalline X-ray diffractometer.The shape of seed crystal according to crucible shape user's needs just, can be right cylinder or cubic cylinder or other polyhedrons without limits.Do not limit the seed crystal size equally, according to crucible size, the cross-sectional area (S of general preferred seed crystal
Seed crystal) with the cross-sectional area (S of growing crystal
Crystal) ratio (S
Seed crystal/ S
Crystal) greater than 70%.If do not use seed crystal, best crucible bottom is shape coning, controls in order to crystal nucleation and grows quality PMNT crystal preferably, and these all are known in the art.
Furnace temperature be 1235~1400 ℃, the maximum temperature gradient of crucible descending direction greater than 50 ℃/cm, guaranteeing raw material fully fusing in crucible, and each component evenly spreads.Crucible after the fusing of inoculation position and being incubated 5~20 hours, is begun growth, generally carry out crucible and descend, can grow and seed crystal direction unanimity and the shape complete PMNT monocrystalline identical with crucible with the speed of 0.1~2mm/hr.Dropping speed of the crucible depends on thermograde in what and the device of quantity, raw material of geomery, the crucible of crucible and insulation situation or the like, and these all are well known to those skilled in the art.If the crucible transfixion can suitably be adjusted thermograde in the stove, slowly lower the temperature, can grow gem-quality crystal equally.
Growth apparatus is not had strict restriction, and general warm terraced subtraction unit all can use.Also can use homemade crucible lowering means, for example we can put into 1-10 platinum crucible with aluminum oxide lagging material homemade monocrystalline decline stove (referring to Fig. 1,2) in growth furnace, carry out crystal growth simultaneously, are beneficial to the large-scale production of PMNT monocrystalline.The heating element of growth furnace is SiC rod or MoSi
2Rod, top temperature can reach 1400 ℃ in the growth furnace, along the maximum temperature gradient of crucible descending direction greater than 50 ℃/cm.Main temperature controlling instruments is the DWK-702 precision temperature controller, temperature-controlled precision reaches ± and 0.5 ℃.The mechanical precision of dropping speed of the crucible generally is controlled at ± and 0.1%, purpose is to grow the uniform PMNT monocrystalline of component.
The present invention compares with the method for solubility promoter growth PMNT monocrystalline, and its advantage is that 1. owing to utilize seed crystal to carry out crystal growth, the macroscopic defects of PMNT monocrystalline is few, perfection of crystal good [Fig. 3].2. because growth raw material is enclosed in the platinum crucible, PbO can not volatilize, and can not cause environmental pollution.3. because growth raw material is enclosed in the platinum crucible, and the PMNT crystalline component of being grown is even, can not depart from its chemical constitution, also can not produce burnt green stone phase, the crystalline piezoelectric property is good.4. crystal growth equipment is simple, and growthing process parameter is controlled easily, and the PMNT crystalline homogeneity of growth, repeatability, consistence are all relatively good.5. because a plurality of crucibles can carry out crystal growth simultaneously, so the production efficiency height is suitable for the large-scale production diameter greater than 40mm, length is greater than the PMNT crystal of 60mm.
For further understanding substantive distinguishing features of the present invention and obvious improvement, further specify the present invention with reference to the accompanying drawings in conjunction with the embodiments, apparent embodiment only supplies illustration purpose, limits the present invention absolutely not.
Embodiment 1.
PbO with high-purity 99.99%, MgO, Nb
2O
5, TiO
2And Pb
3O
4Powder, be made into mixed powder with the 0.60PMN-0.40PT ratio, and then the mole ratio of sneaking into 0.60PMN-0.40PT and PbO is 100: 10 solubility promoter PbO, and cylindrical, the bottom of directly the powder that mixes being put into top and be diameter 10mm are that the cone shape platinum crucible carries out crystal growth.In the monocrystalline decline stove, be 100 ℃/cm along the maximum temperature gradient of crucible descending direction, during growth without the PMNT seed crystal.Melt powder under 1295 ℃ of temperature, be incubated after 5 hours, the speed decline crucible with 0.1mm/hr grows the PMNT crystal and has tetragonal.
Embodiment 2
PbO with high-purity 99.99%, MgO, Nb
2O
5, TiO
2And Pb
3O
4Powder is with 0.76PMN-0.24PT and Pb
3O
4The ratio that is 99: 1 is made into mixed powder, and ball milling made its thorough mixing in 8 hours, and under 1200 ℃ of conditions, solid state sintering becomes the polycrystalline compound of 0.76PMN-0.24PT and PbO, the ground and mixed material, and with powder through hydrostatic or to be molded into density be 6.5g/cm
3Briquetting.Putting it into double-deck wall thickness then is that 0.12mm, diameter are in the 25mm platinum crucible, and<001〉direction cylindrical seed crystal is put into the bottom of crucible, with cross-sectional area S
Seed crystal/ S
CrystalBe that 85% ratio enlarges growth PMNT crystal.Maximum temperature gradient at the crucible descending direction is in the monocrystalline decline stove of 80 ℃/cm, and the top small portion of fusing briquetting material and seed crystal was incubated after 8 hours under 1292 ℃ of temperature, and the speed decline crucible with 0.2mm/hr grows the PMNT monocrystalline.The PMNT crystalline dielectric properties with trigonal crystal structure of being grown are seen Fig. 4, its piezoelectric constant d
33Be about 1050pC/N, DIELECTRIC CONSTANT is about 3000 under the normal temperature.
Embodiment 3.
PbO with high-purity 99.99%, MgO, Nb
2O
5, TiO
2Powder with 0.67PMN-0.33PT chemical formula preparation mixed powder, is put into the logical oxygen of imitation frosted glass stove then and is heated to making powder fusing and thorough mixing more than 1340 ℃, is cooled to the polycrystalline sintered material then, with its starting raw material as crystal growth.In monocrystalline decline stove, putting into 6 cross sections is 40 * 40mm
2, long tetragonal prism for 300mm platinum crucible, the crystallization direction of its seed crystal be<001 〉, be incubated 12 hours after furnace temperature risen to 1400 ℃, the dropping speed of the crucible with 0.8mm/hr carries out crystal growth then.The PMNT crystalline dielectric and the piezoelectric property of being grown are referring to Fig. 5 and 6.Use quasistatic d
33Survey meter records the piezoelectric constant d of monocrystalline
33About 3000pC/N records the electromechanical coupling factor k of PMNT monocrystalline with resonance antiresonance method
33Be 90%, referring to figure.
Embodiment 4.
PbO with high-purity 99.99%, MgO, Nb
2O
5, TiO
2Powder is mixed with the starting raw material of the mixed powder of 0.65PMN-0.35PT as crystal growth.In monocrystalline decline stove, put into the cylindrical platinum crucible that 4 diameters are 50mm, with cross-sectional area S
Seed crystal/ S
CrystalBe that 70% ratio enlarges growth PMNT crystal, the crystallization direction of seed crystal is<111 〉.Insulation is 10 hours after being warming up to 1430 ℃, and the dropping speed of the crucible with 1.5mm/hr carries out crystal growth then.The PMNT crystalline dielectric properties with tetragonal of being grown are seen Fig. 7, and its DIELECTRIC CONSTANT is about 4000 under the room temperature.
Can grow piezoelectric constant d with Bridgman-Stockbarge method for growing PMNT crystalline preparation method provided by the invention as can be seen by embodiment
33Greater than 3000pC/N, electromechanical coupling factor k
33It is 90% high quality P MNT monocrystalline.Can solve the difficulty of relaxor ferroelectric monocrystal growth, realize the large-scale industrial production of PMNT monocrystalline.PMNT monocrystalline that not only can the stable growth large-size high-quality, and can satisfy the PMNT monocrystalline of hi-tech application requiring such as ultra sonic imaging and high strain driving mechanism.