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Hydrothermal synthesis and properties of BaPb1−xBixO3
Journal of Ciystal Growth 79 (1986) 219—222 North-Holland, Amsterdam
219
HYDROTHERMAL SYNTHESIS AND PROPERTIES OF BaPb1 ~Bi~O3 -
Shin-ichi HIRANO and Seiji TAKAHASHI Department of Applied Chemistry, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku~Nagoya 464, Japan
Superconducting BaPb1 ~Bi~O3 (BPB) singie crystals can be grown hydrothermally in KCI solution. In the present work, the solubility of BPB in KC1 solution was measured in order to understand and improve the hydrothermal growth technique. It was found that the solubility increased with temperature, pressure and concentration of KCI solution, and decreased with increase in the composition x under the same hydrothermal conditions. The optimum solubility and solubility difference to grow large and euhedral crystals were determined to be about 3% and 0.7%, respectively. Hydrothermally grown single crystals of BaPb075Bi025O3 showed a transition temperature 1~of 11.7 K for the superconducting state and a narrowest temperature width, 1~,of 1.8 K for the transition.
1. Introduction It was found by Sleight et a!. in 1975 that the solid solution system between BaPbO3 (metallic electric conductor) and BaBiO3 (semiconductor) shows superconductivity in the narrow composition range of 0.05 ~ x ~ 0.30 for BaPb1_~Bi~O3 (BPB) [1]. 7~,the onset to the superconducting state, has been reported to be around 13 K on the basis of electrical resistivity for a polycrystalline specimen with the composition x = 0.25. This 1~ value is the highest among the superconductors without including a transition element, and is also very high for superconductive oxides, including MXWO3 and Li1 + ~Ti2 x°4~ Thanh et al. reported that in the superconductive composition range this system yielded seniimetallic material with a carrier density of the order of 1021 cm which is exceptionally low for superconductors with a high T~ [2]. The Fermi energy EF and the density of states N(EF) were calculated by Tani et al. [3] using Thanh’s results. Their results revealed that the absolute value N( EF) was orders about 1021 states/eV 3 which wasofone to two of magnitude cm smaller than that of the usual high 7~superconductors. It has been considered that high 7~superconductors were required to have both a strong electron—phonon interaction and a large N(EF) on the basis of the BCS theory and the strong-cou—
~
pling theory, but these data suggest that the superconductivity of this system may be attributable to other mechanisms. Such results have been observed on polycrystalline samples, which show a broad transiflon from the normal to the superconducting state as measured by Khan et a!. [4]. Itoh et a!. showed that the specific anomaly at 7~could not be observed on these polycrystalline samples [5]. These problems have been understood to be caused by inhomogeneity or by the grain boundary effects in polycrystalline specimens. Demands to grow homogeneous and wellqualified single crystals of BPB have been increasing greatly in order to characterize the intrinsic superconductive features in this oxide. BPB single crystals have been grown by flux methods above 9000 C [6—10].The superconducting transition of crystals grown by flux methods, however, was unfortunately broad. The results were considered to be caused by the structural transition and oxygen deficiency in BPB crystals grown at ternperatures above 5000 C. We reported that single crystals below of BPB500°Cand could be grown by a hydrothermal method the transition temperature width was the narrowest among the single crystals so far [11]. This paper describes the solubility of BPB in the KC1 hydrothermal solution to determine the optimum growth condition and the property of BPB single crystal.
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
220
S. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
2. Experimental On the basis of the growth experiment of BPB
bi!ity of BPB in this hydrothermal so!ution was measured by a weight-!oss method. Weighed sing!e crystals grown hydrotherma!ly were sealed hermetically into a go!d capsule, 3.0 mm in outer diameter, 0.15 mm thick and 66 mm in length with KC1 so!ution as a so!vent. The sea!ed capsule was placed in a test tube type pressure vesse! and was subjected to gradient. hydrothermal treatment without a temperature The temperature was measured with a calibrated sheathed thermocouple set inside the pressure vessel. After an experimental run, the pressure vessel was quenched in cold water. The dependence of the solubility on compositions of BPB was measured at hydrothermal ternperatures of 350 to 450°Cand 1000 kg/cm2 in 4.5m KC1 solution using the crystals with x = 0, 0.20, 0.25 of BPB. The dependence of the solubility on concentrations of solvents was determined at 450°Cand 1000 kg/cm2 in KC1 solution with concentrations of 1.Om to 4.5rn using a crystal of BPB with x = 0.25. The relation of the solubility to the hydrothermal pressures was measured at 450°C and pressures of 500 to 1250 kg/cm2 in 4.5m KC1 solution using crystals of BPB with x = 0.25. A duration of 3 days was found by the preliminary work to be long enough to reach the equilibrium in this system.
3. Results and discussions 3.1. Solubility of BPB Solubility—temperature curves of BPB, with x 0, 0.20, 0.25 under hydrothermal conditions, are shown in fig. 1. The solubility of BPB in hydrothermal solution increased with temperature of hydrothermal treatment and increased steeply from 400°C to 450°C. We reported [11] that =
5.0
I
Cl)
0 0
I
350
400 450 Temperature, ~C
.
Fig. 1. Solubihty—temperature curves for BaPb in 1 — Bi 03 2with (•) x = 0, (U) x = 0.20 andKCI (A)solution. x = 0.25, at 1000 kg/cm 4.5m
many small crystals were grown at 450°Cin the growth zone of a gold capsule, while a few large crystals were grown at 400°C.The solubility data indicate that the degree of supersaturation at 450°Cwas much higher than that at 400°Cwith a temperature difference. Thus many small crystals can be grown spontaneously on the walls of gold capsules due to high supersaturation. The solubility was also found to be lower with an increase in x at a fixed temperature and pressure. The higher growth temperature was required to grow large and euhedral crystals with an increase in x, which is consistent with the decrease in solubility with increasing x shown in fig. 1. Fig. 2 shows the Van ‘t Hoff relation of solubility. The linear relation between log S and 1/T demonstrates that BPB dissolves in the KC1 hydrothermal solution by the same dissolution mechanism under hydrothermal conditions with a dissolution enthalpy of about 9.6 kcal/mol. Fig. 3 shows the relationship between the solubility and concentration of KC1 solutions and solubility increases with concentration. The dependency of the solubility on pressures is shown in fig. 4 and solubility increases with pressure, indicating a solubility increase in the higher density of solution. This fact suggests that the dissolution reaction involves decreasing the volume of the solute species.
LI
S. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
Temperature, ~C 400
450
221
50
350
I
4.0
I
-1.5
500
-2.0 I
I
I
1.4
1.5 3/T
1.6
150
1000
1250
Pressure,kg/cm2
Fig. 4. Solubility—pressure curve for BaPb 075Bi025 03 at 450°C in 4.5m KC1 solution.
10
Fig. 2. The Van ‘t Hoff relation of solubility of BaPbi ~Bi~ 22 with (S) x =0, (U) xin= 4.5m 0.20 KCI and solution, (A) x = 0.25, at 1000 kg/cm
3.2. Superconducting property of grown single crystals Fig. 5 shows susceptibility—temperature curves for single crystals of BPB with x = 0.20 and 0.25. The data on a single crystal grown by a flux method are also shown. The transition temperature, 7~,and the transition width, 47~,of single crystals of BPB with x = 0.20 were 6.8 and 1.8 K, and with x = 0.25 they were 11.7 and 1.8 K,
respectively. It was found that 1~ depended strongly on x. Therefore, precise control of the composition of single crystals of BPB is required in order to grow single crystals of BPB with high T~.Fortunately, the hydrothermal method has been found to be promising to grow homogeneous BPB single crysta!s)with the desired composition [11]. The transition from the normal state to the superconducting state of single crystals grown by a flux method was very broad with a larger ~ value, which has been attributed to inhomogeneity and oxygen deficiency in the grown crystals [12].
I ____________ 0
I
0
I
I
III
3455789101112131415
I
1.0 2.0 3.0 4.0 Concentration of KCI soin rn
111)111
5.0
Fig. 3. Dependence of solubility on concentration 2. of KCI solution at 450°C and 1000 kg/cm
Temperature,K .
.
..
Fig. 5. Susceptibility—temperature curves for the single crystals of BaPb 1~Bi~03with: (a) x 0.25 grown hydrothermally; (b) x = 0.20 grown hydrothermally; method [12]. (c) x 0.29 grown by flux
222
5. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
In contrast, the transition is very sharp and the narrowest among the data so far published on single crystals by the hydrothermal method. The result indicates that hydrothermally grown single crystals of BPB are homogeneous and free from
with slight deviations from x = 0.25. Precise control of the composition is required to reach a high 7~in homogeneous single crystals. A hydrothermally grown single crystal of BaPb075Bi025 03 showed a tr4nsition temperature
oxygen defects due to growth below 500°C, above which the oxygen deficiency has been known to be inevitable, leading to the broad transition, The same sharp transition was also observed on single crystals of BPB produced by hydrothermal growth in NaC1 solution. The results show the 2~site is not thethat major substitution K~in a Ba as reported by Chu effect on theofsharp transition et al. [13].
T~of 11.7 K and the narrowest JiT~of 1.8 K, whose superior properties were attained by the homogeneity and freedom from oxygen deficiency.
Acknowledgements The authors gratefully acknowledge Professor S. Tanaka’s Laboratory (Tokyo University, Tokyo, Japan) for support in measuring the superconducting properties of crystals.
4. Conclusion The solubility of BPB in the hydrothermal solution increased with temperature, pressure and concentration of KC1 solution in hydrothermal treatment. The optimum conditions to grow large euhedral single crystals were as follows; growth temperature of 400°C,z.~Tofabout 30°C(0.7% of solubility difference between the dissolving and growth zones) and pressure of 1000 kg/cm2 in 4.5m KC1 solution. The solubility decreased with an increase of composition x in BPB. This mdicates that a higher growth temperature is required in order to grow BPB crystals with higher x values. A linear relationship was observed in the plot of log S (solubility) versus 1/T, as expected from the Van ‘t Hoff law for the dissolution reaction, with L~Hof 9.6 kcal/mol for the heat of dissolution. Large single crystals of BPB could be grown under such hydrothermal conditions and the transition width of these single crystals was the narrowest among the data so far reported. The transition temperature 7~depends strongly on composition of BPB and decreases abruptly
References [1] A.W. Sleight, J.L. Gillson and P.E. Bierstedt, Solid State Commun. 17 (1975) 27.
[21 T.D. Thanh, A. Koma and S. Tanaka, Appi. Phys. 22 (1980) 205. [3] T. Tani, T. Itoh and S. Tanaka, J. Phys. Soc. Japan 49 Suppl. A (1980) 309. [4] Y. Khan, K. Nahm, M. Rosenberg and H. Willer, Phys. Status Solidi (a) 39 (1977) 79. [5] T. Itoh, K. Kitazawa and S. Tanaka, J. Phys. Soc. Japan 53 (1984) 2668. [6] A. Katsui and M. Suzuki, Japan. J. Appi. Phys. 21 (1982) L157. [7] A. Katsui, Japan. J. Appl. Phys. 21 (1982) L553. [8] A. Katsui, Y. Hidaka and H. Takagi, J. Crystal Growth 66 (1984) 228. [9] G.K. Wertheim, J.P. Remeika and D.N.E. Buchanan, Rev. B26 (1982) 2120. [10] Phys. S.V. Zaitsev-Zotov, A.V. Kuznetsov, E.A. Protasov and V.N. Stepankin, Soviet Phys.-Solid State 26 (1984) 1928. [11] S. Hirano and S. Takahashi, J. Crystal Growth 78 (1986) 408. [12] H. Hasegawa, M. Naito, K. Kitazawa, S. Tanaka, S. Takahashi andJapan, S. Hirano, 24th Basic Ceramic Soc. Meeting, 1986,in:p.Abstracts 162. [13] C.W. Chu, S. Huang and A.W. Sleight, Solid State Commun. 18 (1976) 977.
219
HYDROTHERMAL SYNTHESIS AND PROPERTIES OF BaPb1 ~Bi~O3 -
Shin-ichi HIRANO and Seiji TAKAHASHI Department of Applied Chemistry, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku~Nagoya 464, Japan
Superconducting BaPb1 ~Bi~O3 (BPB) singie crystals can be grown hydrothermally in KCI solution. In the present work, the solubility of BPB in KC1 solution was measured in order to understand and improve the hydrothermal growth technique. It was found that the solubility increased with temperature, pressure and concentration of KCI solution, and decreased with increase in the composition x under the same hydrothermal conditions. The optimum solubility and solubility difference to grow large and euhedral crystals were determined to be about 3% and 0.7%, respectively. Hydrothermally grown single crystals of BaPb075Bi025O3 showed a transition temperature 1~of 11.7 K for the superconducting state and a narrowest temperature width, 1~,of 1.8 K for the transition.
1. Introduction It was found by Sleight et a!. in 1975 that the solid solution system between BaPbO3 (metallic electric conductor) and BaBiO3 (semiconductor) shows superconductivity in the narrow composition range of 0.05 ~ x ~ 0.30 for BaPb1_~Bi~O3 (BPB) [1]. 7~,the onset to the superconducting state, has been reported to be around 13 K on the basis of electrical resistivity for a polycrystalline specimen with the composition x = 0.25. This 1~ value is the highest among the superconductors without including a transition element, and is also very high for superconductive oxides, including MXWO3 and Li1 + ~Ti2 x°4~ Thanh et al. reported that in the superconductive composition range this system yielded seniimetallic material with a carrier density of the order of 1021 cm which is exceptionally low for superconductors with a high T~ [2]. The Fermi energy EF and the density of states N(EF) were calculated by Tani et al. [3] using Thanh’s results. Their results revealed that the absolute value N( EF) was orders about 1021 states/eV 3 which wasofone to two of magnitude cm smaller than that of the usual high 7~superconductors. It has been considered that high 7~superconductors were required to have both a strong electron—phonon interaction and a large N(EF) on the basis of the BCS theory and the strong-cou—
~
pling theory, but these data suggest that the superconductivity of this system may be attributable to other mechanisms. Such results have been observed on polycrystalline samples, which show a broad transiflon from the normal to the superconducting state as measured by Khan et a!. [4]. Itoh et a!. showed that the specific anomaly at 7~could not be observed on these polycrystalline samples [5]. These problems have been understood to be caused by inhomogeneity or by the grain boundary effects in polycrystalline specimens. Demands to grow homogeneous and wellqualified single crystals of BPB have been increasing greatly in order to characterize the intrinsic superconductive features in this oxide. BPB single crystals have been grown by flux methods above 9000 C [6—10].The superconducting transition of crystals grown by flux methods, however, was unfortunately broad. The results were considered to be caused by the structural transition and oxygen deficiency in BPB crystals grown at ternperatures above 5000 C. We reported that single crystals below of BPB500°Cand could be grown by a hydrothermal method the transition temperature width was the narrowest among the single crystals so far [11]. This paper describes the solubility of BPB in the KC1 hydrothermal solution to determine the optimum growth condition and the property of BPB single crystal.
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
220
S. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
2. Experimental On the basis of the growth experiment of BPB
bi!ity of BPB in this hydrothermal so!ution was measured by a weight-!oss method. Weighed sing!e crystals grown hydrotherma!ly were sealed hermetically into a go!d capsule, 3.0 mm in outer diameter, 0.15 mm thick and 66 mm in length with KC1 so!ution as a so!vent. The sea!ed capsule was placed in a test tube type pressure vesse! and was subjected to gradient. hydrothermal treatment without a temperature The temperature was measured with a calibrated sheathed thermocouple set inside the pressure vessel. After an experimental run, the pressure vessel was quenched in cold water. The dependence of the solubility on compositions of BPB was measured at hydrothermal ternperatures of 350 to 450°Cand 1000 kg/cm2 in 4.5m KC1 solution using the crystals with x = 0, 0.20, 0.25 of BPB. The dependence of the solubility on concentrations of solvents was determined at 450°Cand 1000 kg/cm2 in KC1 solution with concentrations of 1.Om to 4.5rn using a crystal of BPB with x = 0.25. The relation of the solubility to the hydrothermal pressures was measured at 450°C and pressures of 500 to 1250 kg/cm2 in 4.5m KC1 solution using crystals of BPB with x = 0.25. A duration of 3 days was found by the preliminary work to be long enough to reach the equilibrium in this system.
3. Results and discussions 3.1. Solubility of BPB Solubility—temperature curves of BPB, with x 0, 0.20, 0.25 under hydrothermal conditions, are shown in fig. 1. The solubility of BPB in hydrothermal solution increased with temperature of hydrothermal treatment and increased steeply from 400°C to 450°C. We reported [11] that =
5.0
I
Cl)
0 0
I
350
400 450 Temperature, ~C
.
Fig. 1. Solubihty—temperature curves for BaPb in 1 — Bi 03 2with (•) x = 0, (U) x = 0.20 andKCI (A)solution. x = 0.25, at 1000 kg/cm 4.5m
many small crystals were grown at 450°Cin the growth zone of a gold capsule, while a few large crystals were grown at 400°C.The solubility data indicate that the degree of supersaturation at 450°Cwas much higher than that at 400°Cwith a temperature difference. Thus many small crystals can be grown spontaneously on the walls of gold capsules due to high supersaturation. The solubility was also found to be lower with an increase in x at a fixed temperature and pressure. The higher growth temperature was required to grow large and euhedral crystals with an increase in x, which is consistent with the decrease in solubility with increasing x shown in fig. 1. Fig. 2 shows the Van ‘t Hoff relation of solubility. The linear relation between log S and 1/T demonstrates that BPB dissolves in the KC1 hydrothermal solution by the same dissolution mechanism under hydrothermal conditions with a dissolution enthalpy of about 9.6 kcal/mol. Fig. 3 shows the relationship between the solubility and concentration of KC1 solutions and solubility increases with concentration. The dependency of the solubility on pressures is shown in fig. 4 and solubility increases with pressure, indicating a solubility increase in the higher density of solution. This fact suggests that the dissolution reaction involves decreasing the volume of the solute species.
LI
S. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
Temperature, ~C 400
450
221
50
350
I
4.0
I
-1.5
500
-2.0 I
I
I
1.4
1.5 3/T
1.6
150
1000
1250
Pressure,kg/cm2
Fig. 4. Solubility—pressure curve for BaPb 075Bi025 03 at 450°C in 4.5m KC1 solution.
10
Fig. 2. The Van ‘t Hoff relation of solubility of BaPbi ~Bi~ 22 with (S) x =0, (U) xin= 4.5m 0.20 KCI and solution, (A) x = 0.25, at 1000 kg/cm
3.2. Superconducting property of grown single crystals Fig. 5 shows susceptibility—temperature curves for single crystals of BPB with x = 0.20 and 0.25. The data on a single crystal grown by a flux method are also shown. The transition temperature, 7~,and the transition width, 47~,of single crystals of BPB with x = 0.20 were 6.8 and 1.8 K, and with x = 0.25 they were 11.7 and 1.8 K,
respectively. It was found that 1~ depended strongly on x. Therefore, precise control of the composition of single crystals of BPB is required in order to grow single crystals of BPB with high T~.Fortunately, the hydrothermal method has been found to be promising to grow homogeneous BPB single crysta!s)with the desired composition [11]. The transition from the normal state to the superconducting state of single crystals grown by a flux method was very broad with a larger ~ value, which has been attributed to inhomogeneity and oxygen deficiency in the grown crystals [12].
I ____________ 0
I
0
I
I
III
3455789101112131415
I
1.0 2.0 3.0 4.0 Concentration of KCI soin rn
111)111
5.0
Fig. 3. Dependence of solubility on concentration 2. of KCI solution at 450°C and 1000 kg/cm
Temperature,K .
.
..
Fig. 5. Susceptibility—temperature curves for the single crystals of BaPb 1~Bi~03with: (a) x 0.25 grown hydrothermally; (b) x = 0.20 grown hydrothermally; method [12]. (c) x 0.29 grown by flux
222
5. Hirano, S. Takahashi
/
Hydrothermal synthesis and properties of BPB
In contrast, the transition is very sharp and the narrowest among the data so far published on single crystals by the hydrothermal method. The result indicates that hydrothermally grown single crystals of BPB are homogeneous and free from
with slight deviations from x = 0.25. Precise control of the composition is required to reach a high 7~in homogeneous single crystals. A hydrothermally grown single crystal of BaPb075Bi025 03 showed a tr4nsition temperature
oxygen defects due to growth below 500°C, above which the oxygen deficiency has been known to be inevitable, leading to the broad transition, The same sharp transition was also observed on single crystals of BPB produced by hydrothermal growth in NaC1 solution. The results show the 2~site is not thethat major substitution K~in a Ba as reported by Chu effect on theofsharp transition et al. [13].
T~of 11.7 K and the narrowest JiT~of 1.8 K, whose superior properties were attained by the homogeneity and freedom from oxygen deficiency.
Acknowledgements The authors gratefully acknowledge Professor S. Tanaka’s Laboratory (Tokyo University, Tokyo, Japan) for support in measuring the superconducting properties of crystals.
4. Conclusion The solubility of BPB in the hydrothermal solution increased with temperature, pressure and concentration of KC1 solution in hydrothermal treatment. The optimum conditions to grow large euhedral single crystals were as follows; growth temperature of 400°C,z.~Tofabout 30°C(0.7% of solubility difference between the dissolving and growth zones) and pressure of 1000 kg/cm2 in 4.5m KC1 solution. The solubility decreased with an increase of composition x in BPB. This mdicates that a higher growth temperature is required in order to grow BPB crystals with higher x values. A linear relationship was observed in the plot of log S (solubility) versus 1/T, as expected from the Van ‘t Hoff law for the dissolution reaction, with L~Hof 9.6 kcal/mol for the heat of dissolution. Large single crystals of BPB could be grown under such hydrothermal conditions and the transition width of these single crystals was the narrowest among the data so far reported. The transition temperature 7~depends strongly on composition of BPB and decreases abruptly
References [1] A.W. Sleight, J.L. Gillson and P.E. Bierstedt, Solid State Commun. 17 (1975) 27.
[21 T.D. Thanh, A. Koma and S. Tanaka, Appi. Phys. 22 (1980) 205. [3] T. Tani, T. Itoh and S. Tanaka, J. Phys. Soc. Japan 49 Suppl. A (1980) 309. [4] Y. Khan, K. Nahm, M. Rosenberg and H. Willer, Phys. Status Solidi (a) 39 (1977) 79. [5] T. Itoh, K. Kitazawa and S. Tanaka, J. Phys. Soc. Japan 53 (1984) 2668. [6] A. Katsui and M. Suzuki, Japan. J. Appi. Phys. 21 (1982) L157. [7] A. Katsui, Japan. J. Appl. Phys. 21 (1982) L553. [8] A. Katsui, Y. Hidaka and H. Takagi, J. Crystal Growth 66 (1984) 228. [9] G.K. Wertheim, J.P. Remeika and D.N.E. Buchanan, Rev. B26 (1982) 2120. [10] Phys. S.V. Zaitsev-Zotov, A.V. Kuznetsov, E.A. Protasov and V.N. Stepankin, Soviet Phys.-Solid State 26 (1984) 1928. [11] S. Hirano and S. Takahashi, J. Crystal Growth 78 (1986) 408. [12] H. Hasegawa, M. Naito, K. Kitazawa, S. Tanaka, S. Takahashi andJapan, S. Hirano, 24th Basic Ceramic Soc. Meeting, 1986,in:p.Abstracts 162. [13] C.W. Chu, S. Huang and A.W. Sleight, Solid State Commun. 18 (1976) 977.