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Hydrothermal crystallisation and some properties of bismuth titanates
530
Journal of Crystal Growth 13114 (1972) 530--534 © North'Holland Publishin ,, Co.
HYDROTHERMAL CRYSTALLISATION AND SOME PROPERTIES OF B I S M U T H TITANATES M. L BARSUKOVA, V. A. KUZNETSOV, A. N. LOBACHEV and Yu. V. SHALDIN
Institute of Crystallography, Academy of Sciences of the U.S.S.R., Lenin Pr., V-333, Moscow, U.S.S. This article gives the results of investigations into hydrothermaI crystallisation in the BizOa-TiO~ and a study of the non-linear optical properties of the synthesized crystals.
1. Introduction The BizO3-TiO2 system has been the subject of investigation more than once because of the unique characteristics o f the bismuth-titanate series. N~vertheless until recently there have been differences of opinion on the number and composition of individual compounds in this system. According to ref. 1, there exist nine titanates of bismuth with high dielectric permittivities. Subsequent work s'a) does not support this co,clusion. The existence of only three titanates of bismuth is firmly established: Bi.~Ti3Ot2, Bi2Ti4Oll and Ti-silleni:e. More than one opinion exists about the composition of the latter: Bi: 4TiOas2), Bil 2TiO 2o¢) BiaTiO t 43), and in re,f. 5 siilenite is considered as a solid solution with t~,e ratio BizOa/TiO2 (mol.) from 25:1 to 8:1. There a,-e also indications of the existence of a phase intermediate in composition between Bi4Ti~O~2 and Bi2Ti,Ol l, to which both the formulae Bi2Ti207 ~) and Bi2Ti3092) have been ascribed. One of the reasons for the disagreements indicated above relating to phase-formation in the Bi203-TiO2 system is, apparently, that previous investigations have L~ee~nconducted by differentia! thermal and X-ray structual analysis without isolation of the individual bismuth titanates in the form of single-crystals (except Bi ~Ti 3Or 2). One of the problems before us in the study of crystallisation in the Bi203-T:O~ s3stem was the vecessity of isolating the bismuth tital~.ates in the form of single-crystals, suitable for individua~ investigation by chemical a.~ld X-ray methods.
stem
The second problem was to obtain sufficiently large and optically homogeneous crystals of bismuth titan. ares suitable for studying their non-finear properties. As is known, sillenite crystals (Si-sillenite, Ge-siUenite), which are characterised by high values of ionic (r.-~/2 > 30) and electronic (r/~ > 4) polarisability 4.7) occupy a special place amongst non-linear cubic crystals. By analogy, high values of polarisability may be expected for Ti-sillenite. In the present work special attention was paid to the separate study of crystals of Ti-sillenite and Bi4Ti3012.
2. Experimental The investigations were conducted in steel autoclave,~ of 150 cm a capacity. The starting charge was t~ care. fully blended mix of the chemical reagents Bi2(:~ and TiOa. The ratio Bi203/TiO2 (reel.) was varie~ from 20:1 to 1:6; with large Tie2 content in the char ,', the titanium oxide separated out as an independent hase. The temperature of the experiments was 400-t 3 :C, but below 450 °C the synthesis of bismuth I tnate reaction proceeded very slowly, and, as a rule, or very small crystals formed which were unsuitable fc tudy of their physical characteristics. In a similar v , the filling factor of the autoclaves was not less than ~ --0.8. The choice of solvents which will ensure recrx llisation and production of sufficiently large cry Is of bismuth titanates presents considerable compli, ions. On the basis of previous investigations into crF dlisation of Tie2 and titanates of leadT), we used K solutions as solvents.
XI - 3
H Y D R O T H E R M A L C R Y S T A L L I S A T I O N A N D SOME P R O P E R T I E S OF BISMUTH TITANATES
531
4-
/ 20,
,t0,
a,=O,
lb
t~ Fig. I.
2'0
6'.1
3'0
(o
Mote"/,
6'0
';,b
IkO,/~O, mole 2:'~
sh
'1~l~
~'.,,
Phase relation in the B i 2 0 3 - T i O z - K F - H . , O system. Mono-mineral crystallisation is shown by the hatching.
3. Results
Only three individual compounds, Bi4TiaOi2, Biz Ii4Oit and Ti-sillenite, were formed in the Bi203TiO, system under the conditions employed. The identity of the synthesised compounds was confirmed by cht..~ical, X-ray and optical methods. The region of cr3 "dlisation of the bismuth titanates is shown in fig. I. sillenite is formed in the part of the system rich in ,muth, being practically a single phase when the Tit, content in the starting charge is from 7.5 to 20 )le%. When the TiO2 content is less pale-yellow ele, ated crystals of oxide bismuth Qt-Bi20 a, are formed gether with Ti-sillenite. composition of the Ti-sillenite crystals corresp~ ls to Bi12TiO2o (Bi203, 96.44%; TiO2, 2.16%) ant ioes not depend on the composition of the starting eh; e. These results do not confirm the formation of sol: solutions on the basis of Ti-sillenite under the con itions of our experiments. The Ti-sillenite was in the orm of isometric crystals of yellow, sometimes
reddish colour. When charges enriched with Bi203 (TiO 2 content is 7.5-14.5 mole °~) were used, the facets of tetrahedron (ill), trigontritetrahedron (ll2) and rhombododccahedron (! 10) predominated on the crystals and the facets of cubes (100) were somewhat less strongly developed (fig. 2). With TiO2 content 14.5-20 mole%, the facets of tetrahedron and trigontritetrahedron were most developed, and the facets of cube and rhombododecahedron practically disappeared.
Xl - 3
Fig. 2.
Crystal of Ti-sillenite.
532
M.L. BARSUKOVA, V, A. KUZNETSOV, A. N. LOBACHEV AND YU. V. SHALD|N
The parameters of the elementary cell of the synthesised Bi12TiO2o were a = b = c = 10.15A. The cD'stals appear practically isotropic in polarised light. The refractive index is 2,65. The pycnometric density of the Ti-sillenite crystals is 9.1 g4'cm3, the microhardness, determined on "'PMT-3" equipment on artificial polished sections, is 380 kg/mm 2. The melting temperature of synthesised Ti-sillenite is 880tC. The relative dielectric permitivity of Ti-sillenite, measured on a "'VM-271" instrument of the firm "Tesla'" at a frequency 0.2 MHz, is o f the order 50. The edge of the electron adsorption band, determined by the disappearance of double refraction induced by the electric field, is 400 nm and is displaced towards the longer wavelength part of the spectrum compared to the Ge- and Si-sillenitesg). Bi.~Ti:sOt 2 (Bi,Oa, 77.00/,, o/. TIO2, • 20.80 oYo) begins to cryst~iise, together with Ti-sillenite, in the form o f transparent thin, up to 0.1 mm, tetragonal platelets of light yellow coiour when the TiO2 content in the charge is greater than 20 mole ~/. As the TiO2 in the charge is increased, the quantity of Bi4TisO~2 increases and it becomes practically single-phase in the 55-67 rrole,.%~ TiOz range. Simultaneously, the cr.ystals become thicker. up to 1 mm. Along with the pinacoid (001) a development of facets of a lateral band (101) is obtained on the crystals (fig. 3). -Ihe parameters of the elementary cell of Bi,tTi30~z are a = 5.41 rk, b = 5.45 A,, c = 32.83 ~. The refractive index is 2.59; the pycnometric density is 7.8 g/cm. the mean microhardness is 313 kg/mm 2. A strongly expressed anisotropy of the microhardness from 272 to 364 kg/mm in two mutually perpendicular directions in the plane of the pinacoid is characteristic for Bi~Ti30~z. The temperature of the phase transition of Bi,~Ti3OI2 is 670 °C. The edge of the electron absorption band lies in the regior of 400 nm and in value is near to the absorption band in Ti-sillenite. The electrical resistivity is approximately 10 ~2 ohm cm, and the value of the relative dielectric permitivity = 150. Bi2Ti,~O~x (BizOs, 58.30°/,,; TiO2, 40.80%) is the predominant phase in the range of valaes 75-82 mole TiO 2 and is found as lime-yellow, of~ea greenish transp~trent crystals of two morphological t~,'pes. When there is an exess of Bi203 is the charge ove, the stoichiometric composition plale-like, strongly striated crystals
l
101 t0i
Fig. 3. Crystal of Bi4Ti3Oaz.
210
to
Fig. 4. Platelike crystal of Bi2Ti.LOll.
2i0 100 I~o
010
:_ ,~22._
Fig. 5. Prismatic crystal of Bi2Ti.~O~.
are formed (fig. 4). With B i 2 0 3 : T i O 2 = !:4 charge, or with excess of TiO., the crystals arc prismatic with well developed facets (fig. 5). The metric density of the crystals if 6.1 g/cm 3, tht hardness 758 k g / m m 2. All the synthesised compounds below 500 ~ the form of small crystals, less than 1 mm. Inc the temperature promotes increase in their din, and in the 550-600 °C range the crystals attai of several ram. In the presence of a temperat~ dient along the body of the autoclave in the 550
Xl - 3
a the hortcn0,icr0~re in tse in tsi0ns a size ¢ gra,00 °C
HYDROTHERMAL C R Y S T A L L I S A T I O N AND SOME PROPERTIES OF BISMUTH T1TANATES
re ion simultaneously with synthesis recrystallisation o! he material from the lower to the upper zone of the a~ )clave occurs; then crystals having m a x i m u m size a
u cr a~ it e" p
//
60
)12,
the ~tal size (simultaneously with a lowering of the 3unt of transport o f the material) together with an -ease of the TiO2 content in the crystal provides tence of a lower mobility of titanium oxide com:d with bismuth oxide.
A: .1-1inearproperties o f Ti-sillenite and Bi4TiaO~2 Fo measure the non-linear change of the refractive index of Ti-sillenit¢ which is produced by an electric field, an orientated specimen in the form of a rectangular platelet of dimensions 3.6 x 4 x 0.4 m m was prepared from the single crystals. The electric voltage applicd to previously deposited electrodes of finely dispers~d silver, created a field along the <110>, and the light beam was normal to the (110) surface. Measurement of the dispersion of."controlling" (half wave retardation) voltage u~,~ and At/were made in circularly and linearly polarised light beams. Fig. 6 shows how the effective signal, the magnitude of which determines the values of u ~ and At/changes in both cases. The data from calculations based on the results of measurement in circularly and linearly polarised light are in good agreement with the value indicated above. The dispersion of values of u½~ and At/in Ti-sillenite crystals was investigated in the region from 0.7 to 0.46 l~m. A " S P M - I " monochrometer with a filament lan;D "Cu8-200" was used as the source of monochrom a c radiation. The dependencies u½~(2) and At/(A) we constructed (fig. 7) from the experimental data wi~ account of the relationship for u,~ I°) (the latter is ~gle-valued and determined by the value of the vo ges applied to the crystal and of the alternating an onstant voltages at the output of the photodetector The curve of the dispersion (dotted) of u~x for Kt PO~ crystals is also given for comparison. Noticeab; leviation of the dependence ut~ from a linear law is ,served as the absorption band is approached. Si~ • photoconductivity occurs in melt grown crystals of ;- and Si-sillenites'l), attempts were made to inyes ..;ate the dependence of u½~ on the intensity of ligt and on time at the wavelength 500 nm, but no effec~ associated with photoconductivity were observed.
> E ,t.-.,.
3
:3o 3
,,....
533
,._.,
2,0 4'0
$
4.g
1,0
v
(kV)
Fig. 6. The value of the effective signal at the output of the " F E U " (photomultiplier) as a function of the voltage frequency, to, on a specimen oftitanosillenite.Top line: Circularly polarised; and bottom line: linearly polarised light beam. Abscissa: voltage in kilovolts. Ordinate: the alternating component of the signal .u(ro) and u(2ro) in millivolts.
"~ zo
I ...,f
o6O
" "
o:
t f J
"~
o,~ Wavelength (.[Am)
go
o,':
Fig. 7. Dispersion of the values of the controlling voltage u t ~(0), and of the non-linear refractive index At/(_L) in Ti-sillenite crystals. The dotted curve is the change of ut~ in KHaPO.t crystals. Abscissa: wavelength in microns. Ordinate: value of the controlling voltage uts in kilovolts and of the non-linear refractive index At/in units of l0 m cm/V.
The dispersion of u ~ and At/in dependence on frequency (oz was investigated on these same crystals. The results of the experiment are presented in fig. 8. Weak increase of At/ which exceeds the experimental error is observed as the frequency increases. Bi4Tia012. The non-linear refractive index AI1 was measured on specimens of 2.5 x2.5 x0.3 mm dimensions. Electrodes to which the voltage was applied via needle contacts were deposited on one of the narrow faces. For circularly polarised light bean:, passing along r _ t/aar~ where t/i is the refractive (010), At/ = t/:31"Lt index along the i direction, r is the value of the coeffi-
XI - 3
534
M, L, BARSUKOVA, V, A, KUZNETSOV, A, N , LOBACHEV A N D YU. V, S H A L D I N
three compounds: Ti-siUenite, Bi,Ti3012, BizTi 3n, ~0o are formed in the Bi203-TiO2 system. (2) A number of the physical properties were ~ ter. mined on Ti-sillenite, Bi4TiaO12 and Bi2Ti40~l rys. "~ tals grown to sizes from 3 to 10 ram. 60 (3) The non-linear properties of Ti-sillenitc and Bi4Ti3Ot2 were investigated. 0
$o
> 30
~
x
Acknowledgements
IO I IO t~
.tO 6
Fig, 8, The controlling voltage u ~ (o) and the non-linear refractive index Atl (~) as a function of the applied field, Ordinate: the ~alue of the controlling voltages u~.x in kilovolts and of the non-linear refractive index ~ in 10~° cm/V, Abscissa: fiequeney of the electric fidd in Hz,
cients o f the electro-optical constants.The measurements ~ r e obtained in circularly polarised light at 535nmwavelength. The change or"the effective signal as a function of the field in this case is linear and has a nature similar to that shown in fig. 6, but the tangent of the angle of slope is somewhat tlifferent and is 0.13 x 10-s. The value obtained was c orrected for the initial doul~,le refraction (70 "" IO") of the crystal specimen and ',~naily the value tg ~ = 1.8 x 10-s was obtained. The value obtained for the controlling voltage ui~ = 5,0 kV (correspondingly A,1 = 54x 10 -~° crn/V), which in value i~ near to t~.~. for titanosillenite.
4. Conclusions l l) The hydrothermal method confirms that only
The authors express their thanks to O. G. Un ~0va for the chemical analysis of the titanites of bi~ auth and to T. N. Ivanova for determination o f the ph sical constants. References 1) G. I. Skanavi and A. !. Demeshina, Zh. Eksperim. i Teor. Fiz, 31 (1956) 565. 2) t. N. Belyaev, N. P. Smolyanov and N. R. Kal'nitskii, Zh. Neorgan Khim. 2 (1963) 348. 3) I. E. Speranskaya, I. S. Rez, L. V. Koslova and V. M. Skorikov, lzv. Akad. Nauk SSSR, Ser. Neorgan. Mater. l (1965) 232. 4) S. C. Abrahams, P. B. Jamieson and J. L. Bernstein, J. Chem. Phys. 47 (1967) 4034. 5) I. E. Speranskaya and V. M. Skorikov, Izv. Akad. Nauk USSR, Set. Neorgan. Mater. 2 (1967) 345. 6) E. Aleshin and R. Roy, J. Am. Ceram Soc. 45 (19621 18. 7) B. N. Litvin, Yu. Shaldin and I. E. Pitavranova, Krtslall0grafiya 13 (1968) 1106. 8) V. A. Kuznetsov, J. Crystal Growth 3, 4 (1968) 405. 9) V.N. Batog, V. i. Burkov, V. A. Kizen' and V. M. Sk~rik0v, Kri ~tallografiya 13 (1968) 928. 10) Yu. V. Shaldin, Yu. V. Piscarevskii and Yu. S. Mctl",hikov. Zh. PrikL Spektroscopii 3 (t965) 463. 11) P. V. Lenzo, E. F. Spenser and A. A, Ballman, Phi,, Rev. Letters 19 (1967) 641.
XI - 3
Journal of Crystal Growth 13114 (1972) 530--534 © North'Holland Publishin ,, Co.
HYDROTHERMAL CRYSTALLISATION AND SOME PROPERTIES OF B I S M U T H TITANATES M. L BARSUKOVA, V. A. KUZNETSOV, A. N. LOBACHEV and Yu. V. SHALDIN
Institute of Crystallography, Academy of Sciences of the U.S.S.R., Lenin Pr., V-333, Moscow, U.S.S. This article gives the results of investigations into hydrothermaI crystallisation in the BizOa-TiO~ and a study of the non-linear optical properties of the synthesized crystals.
1. Introduction The BizO3-TiO2 system has been the subject of investigation more than once because of the unique characteristics o f the bismuth-titanate series. N~vertheless until recently there have been differences of opinion on the number and composition of individual compounds in this system. According to ref. 1, there exist nine titanates of bismuth with high dielectric permittivities. Subsequent work s'a) does not support this co,clusion. The existence of only three titanates of bismuth is firmly established: Bi.~Ti3Ot2, Bi2Ti4Oll and Ti-silleni:e. More than one opinion exists about the composition of the latter: Bi: 4TiOas2), Bil 2TiO 2o¢) BiaTiO t 43), and in re,f. 5 siilenite is considered as a solid solution with t~,e ratio BizOa/TiO2 (mol.) from 25:1 to 8:1. There a,-e also indications of the existence of a phase intermediate in composition between Bi4Ti~O~2 and Bi2Ti,Ol l, to which both the formulae Bi2Ti207 ~) and Bi2Ti3092) have been ascribed. One of the reasons for the disagreements indicated above relating to phase-formation in the Bi203-TiO2 system is, apparently, that previous investigations have L~ee~nconducted by differentia! thermal and X-ray structual analysis without isolation of the individual bismuth titanates in the form of single-crystals (except Bi ~Ti 3Or 2). One of the problems before us in the study of crystallisation in the Bi203-T:O~ s3stem was the vecessity of isolating the bismuth tital~.ates in the form of single-crystals, suitable for individua~ investigation by chemical a.~ld X-ray methods.
stem
The second problem was to obtain sufficiently large and optically homogeneous crystals of bismuth titan. ares suitable for studying their non-finear properties. As is known, sillenite crystals (Si-sillenite, Ge-siUenite), which are characterised by high values of ionic (r.-~/2 > 30) and electronic (r/~ > 4) polarisability 4.7) occupy a special place amongst non-linear cubic crystals. By analogy, high values of polarisability may be expected for Ti-sillenite. In the present work special attention was paid to the separate study of crystals of Ti-sillenite and Bi4Ti3012.
2. Experimental The investigations were conducted in steel autoclave,~ of 150 cm a capacity. The starting charge was t~ care. fully blended mix of the chemical reagents Bi2(:~ and TiOa. The ratio Bi203/TiO2 (reel.) was varie~ from 20:1 to 1:6; with large Tie2 content in the char ,', the titanium oxide separated out as an independent hase. The temperature of the experiments was 400-t 3 :C, but below 450 °C the synthesis of bismuth I tnate reaction proceeded very slowly, and, as a rule, or very small crystals formed which were unsuitable fc tudy of their physical characteristics. In a similar v , the filling factor of the autoclaves was not less than ~ --0.8. The choice of solvents which will ensure recrx llisation and production of sufficiently large cry Is of bismuth titanates presents considerable compli, ions. On the basis of previous investigations into crF dlisation of Tie2 and titanates of leadT), we used K solutions as solvents.
XI - 3
H Y D R O T H E R M A L C R Y S T A L L I S A T I O N A N D SOME P R O P E R T I E S OF BISMUTH TITANATES
531
4-
/ 20,
,t0,
a,=O,
lb
t~ Fig. I.
2'0
6'.1
3'0
(o
Mote"/,
6'0
';,b
IkO,/~O, mole 2:'~
sh
'1~l~
~'.,,
Phase relation in the B i 2 0 3 - T i O z - K F - H . , O system. Mono-mineral crystallisation is shown by the hatching.
3. Results
Only three individual compounds, Bi4TiaOi2, Biz Ii4Oit and Ti-sillenite, were formed in the Bi203TiO, system under the conditions employed. The identity of the synthesised compounds was confirmed by cht..~ical, X-ray and optical methods. The region of cr3 "dlisation of the bismuth titanates is shown in fig. I. sillenite is formed in the part of the system rich in ,muth, being practically a single phase when the Tit, content in the starting charge is from 7.5 to 20 )le%. When the TiO2 content is less pale-yellow ele, ated crystals of oxide bismuth Qt-Bi20 a, are formed gether with Ti-sillenite. composition of the Ti-sillenite crystals corresp~ ls to Bi12TiO2o (Bi203, 96.44%; TiO2, 2.16%) ant ioes not depend on the composition of the starting eh; e. These results do not confirm the formation of sol: solutions on the basis of Ti-sillenite under the con itions of our experiments. The Ti-sillenite was in the orm of isometric crystals of yellow, sometimes
reddish colour. When charges enriched with Bi203 (TiO 2 content is 7.5-14.5 mole °~) were used, the facets of tetrahedron (ill), trigontritetrahedron (ll2) and rhombododccahedron (! 10) predominated on the crystals and the facets of cubes (100) were somewhat less strongly developed (fig. 2). With TiO2 content 14.5-20 mole%, the facets of tetrahedron and trigontritetrahedron were most developed, and the facets of cube and rhombododecahedron practically disappeared.
Xl - 3
Fig. 2.
Crystal of Ti-sillenite.
532
M.L. BARSUKOVA, V, A. KUZNETSOV, A. N. LOBACHEV AND YU. V. SHALD|N
The parameters of the elementary cell of the synthesised Bi12TiO2o were a = b = c = 10.15A. The cD'stals appear practically isotropic in polarised light. The refractive index is 2,65. The pycnometric density of the Ti-sillenite crystals is 9.1 g4'cm3, the microhardness, determined on "'PMT-3" equipment on artificial polished sections, is 380 kg/mm 2. The melting temperature of synthesised Ti-sillenite is 880tC. The relative dielectric permitivity of Ti-sillenite, measured on a "'VM-271" instrument of the firm "Tesla'" at a frequency 0.2 MHz, is o f the order 50. The edge of the electron adsorption band, determined by the disappearance of double refraction induced by the electric field, is 400 nm and is displaced towards the longer wavelength part of the spectrum compared to the Ge- and Si-sillenitesg). Bi.~Ti:sOt 2 (Bi,Oa, 77.00/,, o/. TIO2, • 20.80 oYo) begins to cryst~iise, together with Ti-sillenite, in the form o f transparent thin, up to 0.1 mm, tetragonal platelets of light yellow coiour when the TiO2 content in the charge is greater than 20 mole ~/. As the TiO2 in the charge is increased, the quantity of Bi4TisO~2 increases and it becomes practically single-phase in the 55-67 rrole,.%~ TiOz range. Simultaneously, the cr.ystals become thicker. up to 1 mm. Along with the pinacoid (001) a development of facets of a lateral band (101) is obtained on the crystals (fig. 3). -Ihe parameters of the elementary cell of Bi,tTi30~z are a = 5.41 rk, b = 5.45 A,, c = 32.83 ~. The refractive index is 2.59; the pycnometric density is 7.8 g/cm. the mean microhardness is 313 kg/mm 2. A strongly expressed anisotropy of the microhardness from 272 to 364 kg/mm in two mutually perpendicular directions in the plane of the pinacoid is characteristic for Bi~Ti30~z. The temperature of the phase transition of Bi,~Ti3OI2 is 670 °C. The edge of the electron absorption band lies in the regior of 400 nm and in value is near to the absorption band in Ti-sillenite. The electrical resistivity is approximately 10 ~2 ohm cm, and the value of the relative dielectric permitivity = 150. Bi2Ti,~O~x (BizOs, 58.30°/,,; TiO2, 40.80%) is the predominant phase in the range of valaes 75-82 mole TiO 2 and is found as lime-yellow, of~ea greenish transp~trent crystals of two morphological t~,'pes. When there is an exess of Bi203 is the charge ove, the stoichiometric composition plale-like, strongly striated crystals
l
101 t0i
Fig. 3. Crystal of Bi4Ti3Oaz.
210
to
Fig. 4. Platelike crystal of Bi2Ti.LOll.
2i0 100 I~o
010
:_ ,~22._
Fig. 5. Prismatic crystal of Bi2Ti.~O~.
are formed (fig. 4). With B i 2 0 3 : T i O 2 = !:4 charge, or with excess of TiO., the crystals arc prismatic with well developed facets (fig. 5). The metric density of the crystals if 6.1 g/cm 3, tht hardness 758 k g / m m 2. All the synthesised compounds below 500 ~ the form of small crystals, less than 1 mm. Inc the temperature promotes increase in their din, and in the 550-600 °C range the crystals attai of several ram. In the presence of a temperat~ dient along the body of the autoclave in the 550
Xl - 3
a the hortcn0,icr0~re in tse in tsi0ns a size ¢ gra,00 °C
HYDROTHERMAL C R Y S T A L L I S A T I O N AND SOME PROPERTIES OF BISMUTH T1TANATES
re ion simultaneously with synthesis recrystallisation o! he material from the lower to the upper zone of the a~ )clave occurs; then crystals having m a x i m u m size a
u cr a~ it e" p
//
60
)12,
the ~tal size (simultaneously with a lowering of the 3unt of transport o f the material) together with an -ease of the TiO2 content in the crystal provides tence of a lower mobility of titanium oxide com:d with bismuth oxide.
A: .1-1inearproperties o f Ti-sillenite and Bi4TiaO~2 Fo measure the non-linear change of the refractive index of Ti-sillenit¢ which is produced by an electric field, an orientated specimen in the form of a rectangular platelet of dimensions 3.6 x 4 x 0.4 m m was prepared from the single crystals. The electric voltage applicd to previously deposited electrodes of finely dispers~d silver, created a field along the <110>, and the light beam was normal to the (110) surface. Measurement of the dispersion of."controlling" (half wave retardation) voltage u~,~ and At/were made in circularly and linearly polarised light beams. Fig. 6 shows how the effective signal, the magnitude of which determines the values of u ~ and At/changes in both cases. The data from calculations based on the results of measurement in circularly and linearly polarised light are in good agreement with the value indicated above. The dispersion of values of u½~ and At/in Ti-sillenite crystals was investigated in the region from 0.7 to 0.46 l~m. A " S P M - I " monochrometer with a filament lan;D "Cu8-200" was used as the source of monochrom a c radiation. The dependencies u½~(2) and At/(A) we constructed (fig. 7) from the experimental data wi~ account of the relationship for u,~ I°) (the latter is ~gle-valued and determined by the value of the vo ges applied to the crystal and of the alternating an onstant voltages at the output of the photodetector The curve of the dispersion (dotted) of u~x for Kt PO~ crystals is also given for comparison. Noticeab; leviation of the dependence ut~ from a linear law is ,served as the absorption band is approached. Si~ • photoconductivity occurs in melt grown crystals of ;- and Si-sillenites'l), attempts were made to inyes ..;ate the dependence of u½~ on the intensity of ligt and on time at the wavelength 500 nm, but no effec~ associated with photoconductivity were observed.
> E ,t.-.,.
3
:3o 3
,,....
533
,._.,
2,0 4'0
$
4.g
1,0
v
(kV)
Fig. 6. The value of the effective signal at the output of the " F E U " (photomultiplier) as a function of the voltage frequency, to, on a specimen oftitanosillenite.Top line: Circularly polarised; and bottom line: linearly polarised light beam. Abscissa: voltage in kilovolts. Ordinate: the alternating component of the signal .u(ro) and u(2ro) in millivolts.
"~ zo
I ...,f
o6O
" "
o:
t f J
"~
o,~ Wavelength (.[Am)
go
o,':
Fig. 7. Dispersion of the values of the controlling voltage u t ~(0), and of the non-linear refractive index At/(_L) in Ti-sillenite crystals. The dotted curve is the change of ut~ in KHaPO.t crystals. Abscissa: wavelength in microns. Ordinate: value of the controlling voltage uts in kilovolts and of the non-linear refractive index At/in units of l0 m cm/V.
The dispersion of u ~ and At/in dependence on frequency (oz was investigated on these same crystals. The results of the experiment are presented in fig. 8. Weak increase of At/ which exceeds the experimental error is observed as the frequency increases. Bi4Tia012. The non-linear refractive index AI1 was measured on specimens of 2.5 x2.5 x0.3 mm dimensions. Electrodes to which the voltage was applied via needle contacts were deposited on one of the narrow faces. For circularly polarised light bean:, passing along r _ t/aar~ where t/i is the refractive (010), At/ = t/:31"Lt index along the i direction, r is the value of the coeffi-
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534
M, L, BARSUKOVA, V, A, KUZNETSOV, A, N , LOBACHEV A N D YU. V, S H A L D I N
three compounds: Ti-siUenite, Bi,Ti3012, BizTi 3n, ~0o are formed in the Bi203-TiO2 system. (2) A number of the physical properties were ~ ter. mined on Ti-sillenite, Bi4TiaO12 and Bi2Ti40~l rys. "~ tals grown to sizes from 3 to 10 ram. 60 (3) The non-linear properties of Ti-sillenitc and Bi4Ti3Ot2 were investigated. 0
$o
> 30
~
x
Acknowledgements
IO I IO t~
.tO 6
Fig, 8, The controlling voltage u ~ (o) and the non-linear refractive index Atl (~) as a function of the applied field, Ordinate: the ~alue of the controlling voltages u~.x in kilovolts and of the non-linear refractive index ~ in 10~° cm/V, Abscissa: fiequeney of the electric fidd in Hz,
cients o f the electro-optical constants.The measurements ~ r e obtained in circularly polarised light at 535nmwavelength. The change or"the effective signal as a function of the field in this case is linear and has a nature similar to that shown in fig. 6, but the tangent of the angle of slope is somewhat tlifferent and is 0.13 x 10-s. The value obtained was c orrected for the initial doul~,le refraction (70 "" IO") of the crystal specimen and ',~naily the value tg ~ = 1.8 x 10-s was obtained. The value obtained for the controlling voltage ui~ = 5,0 kV (correspondingly A,1 = 54x 10 -~° crn/V), which in value i~ near to t~.~. for titanosillenite.
4. Conclusions l l) The hydrothermal method confirms that only
The authors express their thanks to O. G. Un ~0va for the chemical analysis of the titanites of bi~ auth and to T. N. Ivanova for determination o f the ph sical constants. References 1) G. I. Skanavi and A. !. Demeshina, Zh. Eksperim. i Teor. Fiz, 31 (1956) 565. 2) t. N. Belyaev, N. P. Smolyanov and N. R. Kal'nitskii, Zh. Neorgan Khim. 2 (1963) 348. 3) I. E. Speranskaya, I. S. Rez, L. V. Koslova and V. M. Skorikov, lzv. Akad. Nauk SSSR, Ser. Neorgan. Mater. l (1965) 232. 4) S. C. Abrahams, P. B. Jamieson and J. L. Bernstein, J. Chem. Phys. 47 (1967) 4034. 5) I. E. Speranskaya and V. M. Skorikov, Izv. Akad. Nauk USSR, Set. Neorgan. Mater. 2 (1967) 345. 6) E. Aleshin and R. Roy, J. Am. Ceram Soc. 45 (19621 18. 7) B. N. Litvin, Yu. Shaldin and I. E. Pitavranova, Krtslall0grafiya 13 (1968) 1106. 8) V. A. Kuznetsov, J. Crystal Growth 3, 4 (1968) 405. 9) V.N. Batog, V. i. Burkov, V. A. Kizen' and V. M. Sk~rik0v, Kri ~tallografiya 13 (1968) 928. 10) Yu. V. Shaldin, Yu. V. Piscarevskii and Yu. S. Mctl",hikov. Zh. PrikL Spektroscopii 3 (t965) 463. 11) P. V. Lenzo, E. F. Spenser and A. A, Ballman, Phi,, Rev. Letters 19 (1967) 641.
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