US3640865A

US3640865A - New ferroelectric materials and process of preparation

Info

Publication number: US3640865A
Application number: US27111A
Authority: US
Inventors: Gerald Burns; Edward A Giess; Daniel F O'kane
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1970-04-09
Filing date: 1970-04-09
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08

Abstract

New transparent ferroelectric compositions have been prepared having a tetragonal tungsten-bronze-type crystallographic structure and having the formula x(ANbO3) . (1-x) MNb2O6 where A is at least one alkali metal ion and M is an alkaline earth metal ion and where x can be from 0.12 to 0.50. These materials have large dielectric constants, ( Epsilon ), and linear electro-optic coefficients (r), at room temperature. The value of r is significantly larger than that of LiNbO3. These materials have great potential as light modulators and deflectors.

Description

O United States Patent [151 3,640,865 Burns et al. 1 Feb. 8, 1972 [54] NEW FERROELECTRIC MATERIALS AND PROCESS OF PREPARATION References Cited [72] Inventors: Gerald Burns, Yorktown Heights; Edward UNITED STATES PATENTS A. Giess Somers; Daniel F. OKane, Katonahian of 3,423,686 1/1969 Ballman et al. ..252/62.9 X

[73] Assignee: International Business Machines Corpora- Primary ExaminerJames E. Poer tion, Armonk, NY. Assistant Examiner.l. Cooper [22] Filed: Apr. 9 1970 Att0meyHamfin and Jancm and Hansel L. McGee 21] Appl. No.: 27,111 [57 ABSTRACT Related Application Dam New transparent ferroelectric Compositions have been prepared having a tetragonal tungsten-bronze-type crystallol commuatlomm'paft P 3 y 5, graphic structure and having the formula x(ANb0 (l-x) I 1969, abandoned, which 13 a contlnuanon-ln-pifn 9 MNb O where A is at least one alkali metal ion and M is an al- 3 y 15, 1968, abandoned, whlch 1S kaline earth metal ion and where x can be from 0.12 to 0.50. a commuatlon'm'pal't of 9 7 These materials have large dielectric constants, (e),and linear 1968, abandoned. electro-optic coefficients (r), at room temperature. The value of r is significantly larger than that of LiNbO These materials [52] US. Cl ..252/62.9, 23/302, 23/304 have great potential as light modulate and d fl t [51] Int. Cl. ..C04b 35/00, C04b 35/60 [58] Field of Search ..252/62.9; 23/301, 302, 304 27 Claims, 8 Drawing Figures PAIENmm am:

SHEET 1 BF FIG. 1

40 80 120 160 200 240 TEMPERATURE (C) FIG. 2

x 14 cm I OH x= 6328A O 10 nz2.25 I l D. l a

O 2 05 6 l- O (D 4 5 as o 2/ O: 1 1 1 L 1 l O TEMPERATURE C INVENTORS GERALD BURNS EDWARD A. GIESS DANIEL F. O'KANE ATTORNEY PAIENTEnrEn a ma SHEET 2 OF 5 F l G. 3

1! U0 wmazmmazfi KNbO (SS) KNbO3 MOLE SrNbz e KNbO "SrNb O SYSTEM PHASE DIAGRAM PAIENYEB 19 2 311m 3 OF 5 BONb O 459 q\ PHASE DIAGAM LU BRONZEiSS) BRONZE(SS)+LIQ. A 2 e q u) n: m E 1200 I] E N E KBo Nb O m I l 1100 1083i4 j/KNbO (SS) m KNbO (SS)-1-BRONZE(SS) o 40 so 00 BGNbzOs manure: 'amz 3.640.865

SHEET 5 BF 5 BaNbzoe XAMMW NEW FERROELECTRIC MATERIALS AND PROCESS OF PREPARATION This application is a continuation-in-part of copending and now abandoned patent application Ser. No. 821,779, filed on May 5, 1969 which was a continuation-in-part of copending and now abandoned patent application Serial No. 753,823, filed on July 15, 1968. which was in turn a continuation-inpart of the copending and now abandoned patent application Serial No. 694,916, filed on Jan. 2, 1968.

DESCRIPTION OF THE PRIOR ART It has been the object of considerable research to provide ferroelectric materials of high purity exhibiting useful physical properties. Such materials find ready application in numerous devices well known in the art. Niobate ceramic compositions have been of particular interest to the researcher. These compositions, because of their high dielectric constants and Curie temperatures, below which they are ferroelectric, have been highly considered in piezoelectric devices, capacitors and modulators.

Compositions of this kind which have been described include alkali metal ion metaniobates, for example, those having the chemical formulas NaNbO KNbO and LiNbO alkaline earth metal ion niobates, e.g., those having the chemical formulas BaNb O Ba Nb O and the corresponding compounds of calcium and strontium; and niobates of zinc, cadmium and lead, e.g., those having the chemical formulas Zn Nb O-,, Cd Nb O, Pb Nb O and PbNb O Additionally, mixed metal niobates have also been prepared. In US. Pat. No. 2,864,713 to Brian Lewis, there is shown and described a composition having the general formula (I-X)L2O'XMR2O6 where L is Na or K, M is Cd or Pb, and R is Nb. These materials are found to have the perovskite crystallographic structure.

Another example of mixed niobates is disclosed in US. Pat. No. 2,805,175 to Gilbert Goodman showing principally lead niobate compositions having the general formula (Pb, A )'(NbO where A represents an element selected from the group consisting of Mg, Ca, Ba and Sr and mixtures thereof. However, these materials do not contain any alkali metal oxide. Further, they have in general been found to have the orthorhombic tungsten-bronze crystallographic structure.

While the compositions in the above-cited patents have found use as temperature sensing elements in control apparatii, transducers and capacitor applications, they have in general found little use in electro-optic applications, such as light modulators and deflectors, This is to be expected, since most of these materials are ceramic and are in general not transparent to light.

SUMMARY OF THE INVENTION A group of ferroelectric materials has been prepared, the members of which have the tetragonal tungsten-bronze type structure as opposed to the perovskite-type structure of like materials described in the prior art. By tetragonal is meant that the lattice constants of the crystals (a, and b,,) are equal for a standard deviation of 0.2 percent. These materials have the general formula x(ANbO lx)MNb O where A is at least one metal selected from the group consisting of Li, Na, K, and Rb and M is a metal selected from the group consisting of Ca, Sr and Ba; and where x can be from about 0.12 to 0.50. The preferred range of x is from about 0.12 to about 0.35. Additionally mixed alkali metal analogs are prepared and have the general formula A A ,M Nb O, where A is a first alkali metal ion, A is a second alkali metal ion, M is an alkaline earth metal ion and 0 x l.0. These materials are grown as optically transparent single crystals, thus are suitable for electro-optic applications.

It is an object of the invention to provide a new class of ferroelectric materials which can be used in electro-optic applications.

A further object of the invention is to provide a new class of ferroelectric materials having the tetragonal tunsten-bronze type crystallographic structure.

Another object of the invention is to provide a new class of ferroelectric materials which are transparent to light and which has the general formula x( ANbO lx)MNb,O where A is a metal selected from at least one of the alkali metal, M is a metal selected from an alkaline earth metal, and x can havea value offrom 0.12 to 0.50.

And still another object of the invention is to provide a new class of fenroelectn'c materials which are transparent to light and which has the formula A,A ,M Nb O, where A is a first alkali metal ion, A is a second alkali metal ion different from A, M is an alkaline earth metal ion and O x l .0.

And yet another object of the invention is to provide a method for preparing crystalline single-phased solid solutions of a new class of ferroelectric compositions having the general formula x( ANbO l-x)Mnb O.;, where A is a metal selected from at least one of the alkali metals, M is a metal selected from the alkaline earth metals and x can have a value of from 0.12 to 0.35.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the 10 c.p.s. dielectric constant parallel and perpendicular to the tetragonal c-axis for KSr Nb O,

FIG. 2 shows the DC parallel electro-optic constant (r) plotted against temperature for KSr Nb O,

FIG. 3 shows the phase diagram for the KNbO SrNb O system.

FIG. 4 shows the phase diagram for the KNbO -BaNb O system.

FIG. 5 is the phase diagram for the NaNbO BaNb O system.

FIG. 6 is a ternary diagram indicating the area of ternary melt compositions from which single crystals of the NaNbO;, BaNb O system can be grown.

FIG. 7 is a ternary diagram illustrating the region of ternary melt composition from which single crystals of the ternary system-KnbO;,-NaNbO BaNb O system are grown. The melt compositions ()needed to obtain various pulled crystal compositions are shown.

FIG. 8 is a ternary diagram illustrating the region of ternary melt composition from which single crystals of the ternary system, RbNbO -NaNbO BaNb O are grown. The melt compositions needed to obtain various pulled crystal compositions are shown.

DESCRIPTION OF PREFERRED EMBODIMENTS This invention is based upon a discovery that single-phased solid solutions of transparent ferroelectric materials can be prepared directly from a melt containing the individual constituents. The materials are prepared from appropriate amounts of alkali metal and alkaline earth metal carbonates and niobium oxide. The reaction of the constituents may be characterized by the following equations:

2M00 (1--x)MCO3 (1-2) Nb O (ANbO -(MNb;0 1-3002; gloom 511400:

+ gNbzofi mNbos) mnmo 200, where gumbo -(MNbz0a)=AM2Nb5015- The ferroelectric compositions are prepared from high-purity starting materials. The carbonates, A CO where A is an alkali metal selected from Li, Na, K, and Rb, and MCO where M is an alkaline earth metal selected from Ca, Sr and Ba, contain less than 10 ppm. impurities and the niobium oxide (Nb O used contains less than 0.03 percent Ta and 10 p.p.m. of other impurities. Stoichiometric quantities of the carbonates and oxide are added to a platinum crucible and heated in an oxygen atmosphere to a temperature between about l,l to about l,500 C. to provide a melt. The melt is found to have binary compositions according to the following general formula:

xANbO b.( lx)MNb O whereA is at least one alkali metal ion, M is an alkaline earth metal ion and x can be from 0.12 to 0.98. Preferred melt compositions from which crystalline single-phase solid solutions can be grown, are exemplified by the following systems:

xNaNbO l-x)BaNb O where x=0.77 to 0.15 (mole fractions);

xKNbO b.( lx)BaNb O where x=0.98 to 0.38 (mole fractions), and

xKNbO b.(lx)SrNb O where x=0.98 to 0.12 (mole fractions).

Single crystals which are single-phase solid solutions can be pulled from the above melts with a seed crystal or by seeding on to a Pt-Rh rod. After a sufficient length of crystal is grown, the melt is cooled slowly to room temperature at a rate of about 5 to 15 C. per hour. During the cooling, single crystals of the solid solution composition crystallize from the melt in the crucible.

Alternately,.the compositions may be prepared by heating appropriate amounts of the alkali metal niobate (ANbO and the alkaline earth metal niobate (MNb O in a platinum crucible. The mixture is heated at a temperature between l,l00 to 1,500 C. to provide a melt having the above composition from which single crystals are grown. The resulting reaction is described in the equation below:

ANbO -l-MNb O -*AM l lb O Single crystalline tungsten-bronze type solid solutions grown as products of the above alternate methods and from the above exemplified melt compositions can be characterized as follows:

xNaNbO l-x)BaNb O where x=0.35 to 0.15 mole fractions;

xRbNbO lx)BaNb O where F030 to 0.35 mole frac- 4O xlzifffss bikxlBaNb O where x=0.35 to 0.25 mole fracxiiib, 1-. s.-b.0, where 1:030 to 0.40 mole fracxK l: b b.(lx)SrNb O,-,, where x=0.45 to 0.12 mole fractions.

a b c d Na,co, 20 10 I3 20 B300, 30 4o 42 as N t o, so so 45 4s The values given are in mole percent. The materials prepared by the above generally described methods are found to be transparent ferroelectric materials.

They have Curie temperatures (T in the range of about 585 C. dielectric constants, measured at room temperature, in the range of about 1,000 to 50, and electro-optic constants (r), i.e., (the response of the crystal to a field E along the caxis, with light traveling along the a-axis in the range of l.3 l0"B&8 cm./volt or a half-wave voltage of about 500 volts. This half-wave voltage can be considerably reduced by operating at temperatures somewhat above room temperature as can be seen in FlG. 2. This voltage can also be reduced by suitably 75 doping the crystals so that the transition temperature is brought closer to room temperature. The constant (r) can be abut six or seven times greater than (r) found for LiNbO a material generally considered to be one of the best materials for use on electro-optic devices. Pycnometric density measurements made on the materials indicate densities of about 5.0 g./cc., which corresponds to two molecules of AM Nb O, per tetragonal unit cell.

Additionally ternary compositions have been prepared hav- 0 ing the formula A A',-,M Nb O, where A is a first alkali metal ion, A is a second alkali metal ion and is different from A, and M is an alkaline earth metal ion and 0 x l .0, where A potassium and A sodium.

Illustrative of these ternary compositions are the KNbO NaNbO -BaNb O and RbNbO NaNbO -BaNb O systems. These compositions can also be given the general formula (ANbO (A'NbO ),,(MNb O where A is a first alkalimetal ion, A is a second alkali metal ion difi'erent from A, M is a metal selected from the alkaline earth metals of the periodic table and x is about 1.5 to about 16.3, y is about L6 to about 26.5 and z is about 72.0 to about 94.0. The values of x, y and z are ascertained from the value of the arrowheads shown in FIGS. 7 and 8. For the KNbO -NaNbO BaNb O system it is seen in the ternary phase diagram of FIG. 7, that crystals are pulled from a relative triangular region of diagram with end points near NaBa Nb O K Na Ba Nb O and (NaNbO O The crystals are pulled from melts represented by (0); the arrows show the composition of the pulled crystal from each melt. Crystals pulled from the indicated melt composition region are found to have the tetragonal or orthorhombic tungsten-bronze type structure which usually have higher BaNb O and lower KNbO concentrations and only slight changes in the NaNbO content. Within the triangular region the shaded area contains compositions with a tetragonal tungsten bronze structure, and outside the shaded area the structure is an orthorhombic tungsten-bronze. In a preferred embodiment of the invention, crystals are pulled from a melt having a composition of K,- Na Ba Nb O where 0.5 x 0.9 to obtain the tetragonal tungsten-bronze structure. Crystals pulled from the melt compositions near (KNbO ),.,(NaNbO )BaNbO are also found to be tetragonal bronze crystals.

For the RbNbO -NaNbO -BaNb O ternary system, see FIG. 8, orthorhombic tungsten bronze crystals are produced along the arrows from melt compositions represented by (0) in the triangular area beneath the dashed line and bounded by NaBa Nb 0l5, Rb =,Na Ba Nb O, and (NaNbO ,,,(BaNb 0 The pulled crystals usually have higher BaNb O lower RbNbO and slight changes in the NaNbO concentrations. For example, a melt of (966.7] can be used to obtain a single crystal of (RbNb0 (NaNbO (BaNb This crystal had a Curie temperature of 558 C. and the microtwins disappeared near 240 C. Cooling below 300 C. with pressure applied along the [I00] direction of the orthohombic cell results in the removal of microtwins.

Crystals as pulled or grown from the melt compositions are found to have a higher Na-to-K. ratio than the melt composition ternary. These ternary metal niobate compositions are found not to have twinned crystal structures or have twinned structures which disappear at relatively low temperatures. These materials have similar electro-optical properties to the above binary compositions.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation.

EXAMPLE I A thoroughly mixed charge of 400' grams comprising 26.9 grams of powdered K CO 1 14.8 grams of powdered SrCO and 258.3 grams of powdered Nb O is loaded in a platinum crucible which is placed in a Czochralski-type crystal pulling apparatus. The crucible and its contents are heated in an oxygen atmosphere at l,500 C. to form a melt of KSr Nb O, A solid solution single crystal was pulled from the melt at approximately 10 mm./hr. After a sufficient length was grown, the crystal was removed from the melt and held about 5 mm. above the melt surface during the cooling of the crucible at 5 to 15 C./hr. Large single crystals (1 l 1 cm?) also grew on the surface of the frozen melt in the platinum crucible. The resulting pulled crystal weighed 20 grams and had a specific gravity of 5.0. The phase diagram shown in FIG. 3 shows no appreciable change in composition of the pulled crystal when the melt composition is KSr Nb O or [(KNb (SrNb O The crystal pulled from KSr Nb O, melt composition exhibited a dielectric anomaly at about 156 C. and peak dielectric constant was 1.4X". The crystal melted at about l,470 Cil0 C.

The homogeneity of the crystals thus prepared was demonstrated by the character of the plots of dielectric constant versus temperature as shown in FIG. 1. FIG. 1 shows the 104 c.p.s.

dielectric constant parallel (e) and perpendicular (e) to the tetragonal c-axis for xsr.Nb o,.. As seen in the figure, e at room temperature is about 10 and peaks above 10. The transition temperature is found to be relatively independent of composition within the solubility range. Above the transition temperature, a Curie law e=C/(TT is found to hold for the crystals measured with C in the 2 to 4 l0 C. range. Hysteresis loops have been measured on a modified Sawyer-Tower circuit at 30 c.p.s. P. (the spontaneous polarization) is p. C/cm. C. below the Curie temperature. At about 160 C.,

the electric field becomes linear for moderate values of E. The room temperature coercive field is about 20,000 v./cm., thus the crystals can be poled easily, i.e., made into a single domain.

FIG. 2 shows the DC parallel electro-optic constant r n,,/n" r, plotted against temperature. This constant describes the response of the crystal to a field E along the caxis, with the light traveling along the a-axis. The indices n and n are the ordinary and extraordinary indices, respectively, and are approximately equal to 2.25. The field induced birefringence as measured at 6,328 A. with a quarter-wave plate and polarizer. The relation between the measured retardation F and r was taken to be ll n r lE/a where l is the optical path length in the crystal and a is wavelength. The room temperature value of r is 1.3 10 cm./volt, as compared to 0. l 8X10 cm./volt for LiNbO In a similar manner many different solid solution compositions in the series were prepared. The dielectric constant at the Curie temperature of the compositions together with the lattice constants (a and c given in angstroms are indicated in the ensuing Table l. The foregoing materials were prepared by mixing appropriate amounts of starting materials and heating them at appropriate temperatures. The melt compositions from which the crystals can be grown is easily gleaned from the phase diagrams of FIGS. 3, 4 and 5.

TABLE I M.P Dielectric a0 co 5:1 'Ic constant at Examples Composition (A.) (A.) C.) 0.) room temp.

2 NaBarNbrom 12.47 3.982 1,420 585 190 KSIzNbsOls... 12.47 3.942 1,470 156 230 KBBaNbsOw" 12.55 4.010 1,405 373 360 RbSr2NbrOrs. 12.51 3.949 1, 407 139 256 6 RbB8QNb5015 12.58 4.024 1,395

EXAMPLE 7 In preparing crystals from ternary melt compositions according to the ternary diagram of FIG. 7, a thoroughly mixed charge of 420 grams comprising 20.64 grams of powdered K CO 3.96 grams of powdered Na CO 147.34 grams of powdered BaCO and 248.06 grams of powdered Nb O is loaded in a platinum crucible which is placed in a Czochralskitype crystal pulling apparatus. The crucible and its contents are heated in an oxygen atmosphere at 1,480 C. to form a ternary melt material having the formula o.a a Ba Nb O (KNbO (BaNb O A single crystal was pulled from the melt at the rate of 7 mm./hr., with a rotation rate of approximately rpm. and in an oxygen atmosphere. The crystal is removed from the melt and held about 5 mm. above the melt surfaces during the cooling of the crucible at a rate of about 5 C./hr., for the first 300 C. and then at 15 C./hr., to room temperature. The crystal had composition corresponding to the following formula:

The resulting pulled crystal had a diameter of about 8 mm. and was 40 mm. long. The crystal weighed 10 grams and had a specific gravity of 5.0. The crystal exhibited a dielectric anomaly at 420 C. and the peak dielectric constant was 190,000. The crystal melted at about 1,4l0 C.i10 C. The crystal has a half-wave retardation voltage of 1,410 volts which is less than half that of the widely used electro-optic material LiNbO In an alternate method a mixture of the niobates of potassium, sodium and barium can be used instead of the carbonates thereof. The niobates of the above metals are prepared by heating a mixture of the metal carbonates and Nb O at 900 to 1,150 C. The metal niobates thus obtained are treated in the same fashion as the metal carbonates above.

In the same fashion disclosed in Example 7 above, several ternary single crystal solid solutions are prepared. Examples 8-2l are given in ensuing Table 2, and Examples 22-28 are given in Table 3. The Curie temperature of the ternary crystal compositions together with the lattice constants (a and c given in angstroms, the melting points of the crystal temperature at which twinning disappears, and the melt compositions used to grow the crystals are given in ensuing Tables 2 and 3. The foregoing materials were prepared by mixing appropriate amounts of starting materials and treating them as in Example 2.

TABLE 2 Composition and properties of crystals pulled from melts of (KNbOs) x (NaNbOa) (B8Nb20u) I Crystal composition from chemical analysis, mole percent Melt composition mole percent Crystal properties Twin structure dlsap- Curie Lattice parameters pears at T., tempera- KNbOa NaNbO; BaNbzOa KNbO; N aNbOa BaNbzOa C. ture, C. as, A. co, A.

Crystal composition from chemical Molt composition mole percent analysis, mole percent Crystal properties Twin structure disap- Curie Lattice parameters pears at T., tempera- KNbO; NeNbO; BflNbzOa KNbOa NaNbO BaNbgO C. turc, C. as, A. Co, A.

10. 10. 80. 03.3 04. B 91.2 Structure O5. 70. 08.3 01.6 90.1 Structure n Psnudo'totmgonnl pnrnmoter, optical interference patterns indicate biaxial symmetry.

No twins at 20 C. 0 BaNbzOu.

TABLE 3 Composition and properties of crystals pulled from melts of (RbNbOa):(NaNbOQABaNbzOo) I Crystal composition from chemical Twin struc- Meas e WW ENBQQ- Crystal properties Melt composition, mole percent analysis mole percent ture disap- Curie Lattice parameters pears at T., temp,

RbNbO NaNbO; BaNbaOa RbNbOs NaNbO; BaNbzOe 0. C. as, A. b0, A. Go, A

06. 7 26. 6 66. 7 1. 5 26. 5 72. 0 240 558 17. 609 17. 633 3. 998 16. 7 16. 6 66. 7 3. 7 18. 4 77. 8 140 505 17. 662 4. 007 16. 7 16.6 66.7 5.1 19.1 75. 8 1 .66 .007 10. 15. 75. 2. 4 20. 0 77. 6 158 496 17. 647 17. 660 4. 005 20. 0 13. 3 66. 7 4. 0 18. 6 77. 4 85 460 17. 665 4. 006 26. 7 0e. 6 66. 7 s. a 03. 2 88. a 15. 10. 75. 4. 2 01. 8 94. 0

8 Crystal from the frozen melt.

It has also been found that when the compositions described 30 will be understood by those skilled in the art that the foregoing TABLE 4 Electrooptic constants T., V X10 Crystals pulled from melts of- C. volt cm./volt e3 1, 410 0. 86 Ko.aNau.2Ba2Nb5015 100 1, 190 0. 48 112 200 640 0. 95 168 NaBazNbrOis 25 1, 570 0. 36 51 KSl'zNbrOrs 25 500 1. 3 400 The phase diagram shown in FIG. 3 was determined for the (KNhO (SrNb O system by differential thermal analysis and X-ray methods. This established the existence of the solid solution region containing the tetragonal tungstenbronzc structure between X=0.l2 and 0.50. in the case of other systems, X-ray analyses showed the presence of a tetragonal tungsten-bronze structure and the limits of solid solution. Also, with the (NaNbO -(BaNbO O crystal growth from a solution of (NaNbO (BaNb O resulted in a crystal composition near (NaNbO (BaNb O as determined by sodium analyses. This further demonstrates the existence of a solid solution region, as indicated in FIG. 5.

In summary, transparent ferroelectric materials have been prepared having the general formulas x(ANbO lx)MNb 0 and A A, ,M Nb O, These materials have a tetragonal tungsten-bronze type structure over a range of A to M concentrations. The materials are ferroelectric along their C-axis with a large room temperature dielectric and linear electro-optic constant.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it

and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

LThe single crystalline ferroelectric composition xKNbO lx)SrNb O where x is from about 0.45 to 0. l2.

2. The single crystalline ferroelectric composition xKNbO (lx)BaNb O where x is from about 0.35 to 0.25.

3. The single crystalline ferroelectric composition xRbNbO lx)SrNb O where x is from about 0.30 to 0.40.

4. The single crystalline ferroelectric composition xRbNbO lx)BaNb O where x is from about 0.30 to 0.35.

5. A single crystalline ternary ferroelectric composition grown from a melt composition in the triangular area defined y NaBa Nb O Rb Na Ba Nb O and (NaNbO ),.,(BaNb 0 as shown in FIG. 8.

6. The single crystalline ternary ferroelectric composition having the formula s)|s.a( 3)fi.3( 2 6)15.4-

7. The single crystalline ternary ferroelectric composition having the formula a)ra.e( a)r:i.r( 2 o)13.3-

8. The single crystalline ternary ferroelectric composition having the formula a)3.s( a)22.o( 2 6)1a.9-

9. The single crystalline ternary ferroelectric composition having the formula s)r.5( a)2o.5( 2 s)12- 10. A method of preparing alkali-metal alkaline earth metal niobate binary compositions having the formula xANbOy (lx)MNb O where A is at least one metal selected from the alkali metals of the periodic table, M is at least one metal selected from the alkaline earth metals of the periodic table and where x is from 0.12 to 0.50, comprising the steps of:

a. intimately mixing an alkali metal carbonate, an alkaline earth metal carbonate, and niobium pentoxide; b. heating the mixture to a temperature from about l,l00

to about l,500 C;

c. forming a liquid phase of the resultant product; and

d. cooling said resultant product to thereby form a single crystal of said alkali metal-alkaline earth metal niobate composition.

11. A method according to claim 10 wherein said alkali metal carbonate is sodium carbonate and said alkaline earth metal carbonate is barium carbonate.

12. A method according to claim 10 wherein said alkali metal carbonate is potassium carbonate and said alkaline earth metal carbonate is strontium carbonate.

13. A method according to claim 10 wherein said alkali metal carbonate is potassium carbonate and said alkaline earth metal carbonate is barium carbonate.

14. A method according to claim 10 wherein said alkali metal carbonate is rubidium carbonate and said alkaline earth metal carbonate is strontium carbonate.

15. A method according to claim 10 wherein said alkali metal carbonate is rubidium carbonate and said alkaline earth metal carbonate is barium carbonate.

16. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xNaNbO l.\:)BaNb O where x is about 0.77 to about 0. l mole fractions.

17. A method according to claim wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xKNbO lx)BaNb O where x is about 0.99 to about 0.38 mole fractions.

18. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xKNbO lx)SrNb O where x is about 0.98 to about 0.12 mole fractions.

19. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a ternary melt composition in the area defined by a, b, c and d as shown in FIG. 6.

20. A method of preparing mixed alkali metals, alkaline earth metal niobate ternary compositions having the general formula (ANbO ),(ANbO MNb O where A is a first alkali metal ion, A is a second alkali metal ion different from A, M is a metal selected from the alkaline earth metals of the periodic table and x is about L5 to about l6.3, y is about L6 to about 26.5 and z is about 72.0 to about 94.0, comprising the steps of:

a. intimately mixing a first alkali metal niobate, a second alkali metal niobate, and an alkaline earth metal niobate;

b. heating the mixture to a temperature of from about l,l00 to about l,500 C; c. forming a liquid phase of the resultant composition, and d. slowly cooling said resultant composition to thereby form a single crystal of said mixed alkali metal alkaline earth metal niobate compositions.

21. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x=3.5, y=22.6 and z=73.9.

22. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x=l6.3, y=8.3, and z==75.4.

23. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x=13.6, y=l3. l, and z=73.3.

24. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where F56 y=l6.l and z=78.3.

25. A method according to claim 20 wherein said first alkali metal niobate is rubidium niobate, said second alkali metal niobate is sodium niobate and said alkaline earth metal niobate is barium niobate and where x=l .5, y=26.5, and F720.

26. A method according to claim 20 wherein said first alkali metal niobate is rubidium niobate, said second alkali metal niobate is sodium niobate and said alkaline earth metal niobate is barium niobate and where x=3.8, y=l 8.4, and z=77.8

27. A method according to claim 20 wherein said single crystal of mixed alkali metals, alkaline earth metal niobate composition is grown from a ternary melt composition in the triangular area defined by NaBa Nb O Rb Na Ba Nb O and (NaNbO BaNb O as shown in H6. 8.

Claims

2. The single crystalline ferroelectric composition xKNbO3.(1-x)BaNb2O6 where x is from about 0.35 to 0.25.
3. The single crystalline ferroelectric composition xRbNbO3.(1-x)SrNb2O6 where x is from about 0.30 to 0.40.
4. The single crystalline ferroelectric composition xRbNbO3.(1-x)BaNb2O6 where x is from about 0.30 to 0.35.
5. A single crystalline ternary ferroelectric composition grown from a melt composition in the triangular area defined by NaBa2Nb5O15; Rb0.65Na0.35Ba2Nb5O15; and (NaNbO3)18(BaNb2O6)82 as shown in FIG. 8.
6. The single crystalline ternary ferroelectric composition having the formula (KNbO3)16.3(NaNbO3)8.3(BaNb2O6)75.4.
7. The single crystalline ternary ferroelectric composition having the formula (KNbO3)13.6(NaNbO3)13.1(BaNb2O6)73.3.
8. The single crystalline ternary ferroelectric composition having the formula (KNbO3)3.5(NaNbO3)22.6(BaNb2O6)73.9.
9. The single crystalline ternary ferroelectric composition having the formula (RbNbO3)1.5(NaNbO3)26.5(BaNb2O6)72.
10. A method of preparing alkali-metal alkaline earth metal niobate binary compositions having the formula xANbO3.(1-x)MNb2O6 where A is at least one metal selected from the alkali metals of the periodic table, M is at least one metal selected from the alkaline earth metals of the periodic table and where x is from 0.12 to 0.50, comprising the steps of: a. intimately mixing an alkali metal carbonate, an alkaline earth metal carbonate, and niobium pentoxide; b. heating the mixture to a temperature from about 1,100* to about 1,500* C; c. forming a liquid phase of the resultant product; and d. cooling said resultant product to thereby form a single crystal of said alkali metal-alkaline earth metal niobate composition.
11. A method according to claim 10 wherein said alkali metal carbonate is sodium carbonate and said alkaline earth metal carbonate is barium carbonate.
12. A method according to claim 10 wherein said alkali metal carbonate is potassium carbonate and said alkaline earth metal carbonate is strontium carbonate.
13. A method according to claim 10 wherein said alkali metal carbonate is potassium carbonate and said alkaline earth metal carbonate is barium carbonaTe.
14. A method according to claim 10 wherein said alkali metal carbonate is rubidium carbonate and said alkaline earth metal carbonate is strontium carbonate.
15. A method according to claim 10 wherein said alkali metal carbonate is rubidium carbonate and said alkaline earth metal carbonate is barium carbonate.
16. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xNaNbO3.(1-x)BaNb2O6 where x is about 0.77 to about 0.15 mole fractions.
17. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xKNbO3.(1-x)BaNb2O6 where x is about 0.99 to about 0.38 mole fractions.
18. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a melt composition having the formula xKNbO3.(1-x)SrNb2O6 where x is about 0.98 to about 0.12 mole fractions.
19. A method according to claim 10 wherein said single crystal of an alkali-metal, alkaline earth metal niobate composition is grown from a ternary melt composition in the area defined by a, b, c and d as shown in FIG. 6.
20. A method of preparing mixed alkali metals, alkaline earth metal niobate ternary compositions having the general formula (ANbO3)x(A''NbO3)y(MNb2O6)z where A is a first alkali metal ion, A'' is a second alkali metal ion different from A, M is a metal selected from the alkaline earth metals of the periodic table and x is about 1.5 to about 16.3, y is about 1.6 to about 26.5 and z is about 72.0 to about 94.0, comprising the steps of: a. intimately mixing a first alkali metal niobate, a second alkali metal niobate, and an alkaline earth metal niobate; b. heating the mixture to a temperature of from about 1,100* to about 1,500* C; c. forming a liquid phase of the resultant composition, and d. slowly cooling said resultant composition to thereby form a single crystal of said mixed alkali metal alkaline earth metal niobate compositions.
21. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x 3.5, y 22.6 and z 73.9.
22. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x 16.3, y 8.3, and z 75.4.
23. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x 13.6, y 13.1, and z 73.3.
24. A method according to claim 20 wherein said first alkali metal niobate is potassium niobate, said second alkali metal niobate is sodium niobate, said alkaline earth metal niobate is barium niobate and where x 5.6, y 16., and z 78.3.
25. A method according to claim 20 wherein said first alkali metal niobate is rubidium niobate, said second alkali metal niobate is sodium niobate and said alkaline earth metal niobate is barium niobate and where x 1.5, y 26.5, and z 72.0.
26. A method according to claim 20 wherein said first alkali metal niobate is rubidium niobate, said second alkali metal niobate is sodium niobate and said alkaline earth metal niobate is barium niobate and where x 3.8, y 18.4, and z 77.8
27. A method according to claim 20 wherein said single crystal of mixed alkali metals, alkaline earth metal niobate composition is grown from a ternary melt composition in the triangular area defined by NaBa2Nb5O15; Rb0.65Na0.35Ba2Nb5O15; and (NaNbO3)18(BaNb2O6)82 as shown in FIG. 8.