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Flux growth of lead scandium tantalate Pb(Sc0.5Ta0.5)O3 and lead magnesium niobate Pb(Mg13 Nb23 )O3 single crystals
Journal of Crystal Growth 50 (1980) 555—556 © North-Holland Publishing Company
LETTER TO THE EDITORS FLUX GROWTH OF LEAD SCANDIUM TANTALATE Pb(Sco
5Ta0 5)03 AND LEAD MAGNESIUM NIOBATE
Pb(Mg113Nb~3)O3SINGLE CRYSTALS N. SETTER and L.E. CROSS Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Received II February I980~manuscript received in fmal form 21 April 1980 Pb(Sc0 5Ta0 5)03 and Pb(Mg1 ,3Nb213)03 crystals were grown from flux. The ferroelectric transition of Pb(Sc0 ~5Ta0.5)03 is 13°Cand e’m~ 18,000.
Lead magnesium niobate and lead scandium tantalate are ferroelectric crystals which exhibit diffuse or broadened phase transitions and a ferroelectric Curie range [1,2]. The tantalate crystal is of special interest, as it has been shown [3] that the state of ordering of the two B site cations in the ABO3 perovskite structure can be modified by suitable thermal treatment. The growth procedure for the Pb(Sc0.5Tao.s)O3 (PST) was as follows: PST powder was first made by wet-mixing stoichiometric proportions of the constituent oxides (PbO, Sc203, Ta205), ball milling for 20 h under alcohol, drying, then calcining at 800°C for 2 h. The calcined powder was then reground and fired at 1300°Cfor 1 h to ensure complete reaction. X-ray diffraction of the fmal powder showed the expected perovskite structure with small traces of a pyrochiore structure phase. The flux that proved most successful was a mixture of PbF2—PbO—B203 used in the ratio by weight PST : PbO : PbF2 : B2O3 = 0.15 :0.40 :0.40 : 0.05. The thermal cycle used was a rapid heating to 1250°C,soaking at that temperature for 4 Ii, cooling at 3°C/h to 1000°C, 5°C/hto 900°C and then 50°C/hback to room temperature. For lead magnesium niobate (PMN), the growth procedure was rather similar as follows: PMN powder was prepared from the mixed oxides. Again a low initial firing was found advantageous in limiting the formation of the undesired pyrochiore phase which can form in this system. The flux used was a PbO : B203 mixture and the ratios were similar
to those chosen by Bonner and Van Uitert [4] for pulling PMN by Kyropoulos technique. The growth temperature cycle in our case was rapid heating to 1150°C soaking for 2 h at that temperature, cooling at 3°C/h to 950°C,5°C/hto 800°C followed by 50°C/hback down to room temperature. In this case the flux was not poured off after growth and the crystals were extracted from the matrix by dissolution in hot dilute nitric acid. The furnace arrangement, which has been described in more detail elsewhere [5], was an alumina tube type, heated by sfficon carbide elements. The growth cycle was programmed by a 5600 /1 Data Track Microprocessor based programmer with blend and master stations controlling a Research Inc. analogue power controller. A listing of the general features of the grown crystals is given in table 1. Rod-like PMN crystals have been previously grown [6] from PbO flux (3 : 2 PbO : PMN) by 25°C/hcooling in the 1200—900°C
Table 1 General description of PST and PMN
555
Property
PST
PMN
Color Shape Edge size (mm) Plane of surface Unit cell size (A) Tc(°C)
Yellow Cube 1—3 (100) 4.073 14
Yellow Cube 1—3 (100) 4.020 —8
556
N. Setter, L.E. Cross/Flux growth of Pb(Sc
0 5Ta0 5)03 and Pb(Mg113Nb213)03 20000
I
I
o~KC
*4
_
U ~0
b’
I
I
j
I
Fig. 1. Crystals of PMN (a) and PST (b) as grown. Scale in cm.
b0
40
~0
0
T(°c)
50
40
60
80
flflkl
11
samples [2]. The transition temperature (T~= 13°C) is also lower than the reported transition for ceramic PST. The transition of PST is sharper than that of PMN, which is a classical relaxor. Also, the frequency dependence of the transition temperature is almost negligible for PST. There is, however, a strong suppression of the dielectric constant with increasing frequency. Curie constant as calculated aboveThis the 5 forfarPST. transitionis temperature 2.5 Xvalues i0 number between the istypical for the order ferroelectric (1 X 10~)and the values for ferroelectric relaxors (4.5 X i0~for PMN). This work was supported by the Office of Naval Research, Grant No. N00014-78-C-0291. Referesices
range. Our crystals have the form of simple cubes with well developed 100 faces (fig. la). The PST crystals have a similar morphology (fig. ib) but the unit cell is smaller than that reported earlier [7], and is similar to that measured on PST powders formed by solid state reaction. The dielectric constant was measured as a function of temperature as a means for evaluating the diffuseness of the phase transition (fig. 2). This was done by measuring the capacitance at frequencies of 1, 10, and 100 kHz with an automatic capacitance bridge (Hewlett Packard 4270A). The 6m~ of PST has a much higher value than the previously reported value of 1400 for polycrystalline
[1] G.A. Smolenskii and A.I. Agranovskaja, Zh. Tech. Fiz. 28
(1958) 1791. [2] G.A. Smolenskii et al., Soviet Phys.-Solid State 1(1959) 150. [31N. Setter and L.E. Cross, J. Mater. Sci., submitted. (1967) 131. [5] L.E. Cross, J.V. B iggers, R.E. Newnham and G.R. Baisch, Annual Report Jait 1 to Dec. 31, 1978, ONR Contract N00014-78-C-029l , Targeted Basic Studies of Ferroelectric and Ferroelastic Crystals for Piezoelectric Transducer
Applications. [6] J.W. Smith, Ph.D. Thesis, The Pennsylvania State Univ. (1967). [7] F. Galasso and W. Darby, Inorg. Chem. 4 (1965) 71.
LETTER TO THE EDITORS FLUX GROWTH OF LEAD SCANDIUM TANTALATE Pb(Sco
5Ta0 5)03 AND LEAD MAGNESIUM NIOBATE
Pb(Mg113Nb~3)O3SINGLE CRYSTALS N. SETTER and L.E. CROSS Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Received II February I980~manuscript received in fmal form 21 April 1980 Pb(Sc0 5Ta0 5)03 and Pb(Mg1 ,3Nb213)03 crystals were grown from flux. The ferroelectric transition of Pb(Sc0 ~5Ta0.5)03 is 13°Cand e’m~ 18,000.
Lead magnesium niobate and lead scandium tantalate are ferroelectric crystals which exhibit diffuse or broadened phase transitions and a ferroelectric Curie range [1,2]. The tantalate crystal is of special interest, as it has been shown [3] that the state of ordering of the two B site cations in the ABO3 perovskite structure can be modified by suitable thermal treatment. The growth procedure for the Pb(Sc0.5Tao.s)O3 (PST) was as follows: PST powder was first made by wet-mixing stoichiometric proportions of the constituent oxides (PbO, Sc203, Ta205), ball milling for 20 h under alcohol, drying, then calcining at 800°C for 2 h. The calcined powder was then reground and fired at 1300°Cfor 1 h to ensure complete reaction. X-ray diffraction of the fmal powder showed the expected perovskite structure with small traces of a pyrochiore structure phase. The flux that proved most successful was a mixture of PbF2—PbO—B203 used in the ratio by weight PST : PbO : PbF2 : B2O3 = 0.15 :0.40 :0.40 : 0.05. The thermal cycle used was a rapid heating to 1250°C,soaking at that temperature for 4 Ii, cooling at 3°C/h to 1000°C, 5°C/hto 900°C and then 50°C/hback to room temperature. For lead magnesium niobate (PMN), the growth procedure was rather similar as follows: PMN powder was prepared from the mixed oxides. Again a low initial firing was found advantageous in limiting the formation of the undesired pyrochiore phase which can form in this system. The flux used was a PbO : B203 mixture and the ratios were similar
to those chosen by Bonner and Van Uitert [4] for pulling PMN by Kyropoulos technique. The growth temperature cycle in our case was rapid heating to 1150°C soaking for 2 h at that temperature, cooling at 3°C/h to 950°C,5°C/hto 800°C followed by 50°C/hback down to room temperature. In this case the flux was not poured off after growth and the crystals were extracted from the matrix by dissolution in hot dilute nitric acid. The furnace arrangement, which has been described in more detail elsewhere [5], was an alumina tube type, heated by sfficon carbide elements. The growth cycle was programmed by a 5600 /1 Data Track Microprocessor based programmer with blend and master stations controlling a Research Inc. analogue power controller. A listing of the general features of the grown crystals is given in table 1. Rod-like PMN crystals have been previously grown [6] from PbO flux (3 : 2 PbO : PMN) by 25°C/hcooling in the 1200—900°C
Table 1 General description of PST and PMN
555
Property
PST
PMN
Color Shape Edge size (mm) Plane of surface Unit cell size (A) Tc(°C)
Yellow Cube 1—3 (100) 4.073 14
Yellow Cube 1—3 (100) 4.020 —8
556
N. Setter, L.E. Cross/Flux growth of Pb(Sc
0 5Ta0 5)03 and Pb(Mg113Nb213)03 20000
I
I
o~KC
*4
_
U ~0
b’
I
I
j
I
Fig. 1. Crystals of PMN (a) and PST (b) as grown. Scale in cm.
b0
40
~0
0
T(°c)
50
40
60
80
flflkl
11
samples [2]. The transition temperature (T~= 13°C) is also lower than the reported transition for ceramic PST. The transition of PST is sharper than that of PMN, which is a classical relaxor. Also, the frequency dependence of the transition temperature is almost negligible for PST. There is, however, a strong suppression of the dielectric constant with increasing frequency. Curie constant as calculated aboveThis the 5 forfarPST. transitionis temperature 2.5 Xvalues i0 number between the istypical for the order ferroelectric (1 X 10~)and the values for ferroelectric relaxors (4.5 X i0~for PMN). This work was supported by the Office of Naval Research, Grant No. N00014-78-C-0291. Referesices
range. Our crystals have the form of simple cubes with well developed 100 faces (fig. la). The PST crystals have a similar morphology (fig. ib) but the unit cell is smaller than that reported earlier [7], and is similar to that measured on PST powders formed by solid state reaction. The dielectric constant was measured as a function of temperature as a means for evaluating the diffuseness of the phase transition (fig. 2). This was done by measuring the capacitance at frequencies of 1, 10, and 100 kHz with an automatic capacitance bridge (Hewlett Packard 4270A). The 6m~ of PST has a much higher value than the previously reported value of 1400 for polycrystalline
[1] G.A. Smolenskii and A.I. Agranovskaja, Zh. Tech. Fiz. 28
(1958) 1791. [2] G.A. Smolenskii et al., Soviet Phys.-Solid State 1(1959) 150. [31N. Setter and L.E. Cross, J. Mater. Sci., submitted. (1967) 131. [5] L.E. Cross, J.V. B iggers, R.E. Newnham and G.R. Baisch, Annual Report Jait 1 to Dec. 31, 1978, ONR Contract N00014-78-C-029l , Targeted Basic Studies of Ferroelectric and Ferroelastic Crystals for Piezoelectric Transducer
Applications. [6] J.W. Smith, Ph.D. Thesis, The Pennsylvania State Univ. (1967). [7] F. Galasso and W. Darby, Inorg. Chem. 4 (1965) 71.