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Absorption of hydrogen by vanadium-rich VTi-based alloys
64
Journal
Absorption V-Ti-based A. Kagawa, Department
of the Less-Common
Metals, 172-174
(1991) 64-70
of hydrogen by vanadium-rich alloys E. Ono, T. Kusakabe
of Materials
Science
and Y. Sakamoto
and Engineering,
Nagasaki
University,
Nagasaki
852
(Japan)
Abstract The pressure-composition isotherms of dihydride formation in (Vi _ XTi,), by M, (X = 0.1-0.2; M = Al, Si, Zr, Cr, Fe, Co, Ni; y = 0.01-0.1) alloys were determined at temperatures between 273 and 433 K and hydrogen pressures up to 3 MPa. The effect of absorption-desorption cycles on the hydriding properties were also examined, together with an evaluation of the pulverization resistance. It was found from the experiment on hydriding cycles that the V,,Ti,,, alloys with chromium showed a good pulverization resistance and no significant deterioration of the effective hydrogen content, although the hysteresis factor was relatively large.
1. Introduction Dihydrides of vanadium-based b.c.c. solid solution alloys have been the subject of recent investigations because of their potential for use in metal hydride heat pumps and other similar applications [l-3]. Generally, the b.c.c. group V metals can be made to react rapidly with hydrogen at room temperature by alloying with a small amount of a second metal [4]. From a study of the monohydride (/?)edihydride (7) phase equilibrium for the vanadium-rich V-Ti-based alloys, Libowitz and coworkers [l, 31 have shown that the enthalpy and entropy changes for dihydride formation have relatively high values compared to those of LaNi, hydrides and that the alloys have flexibility in the choice of their thermodynamic properties through modification of the alloy composition. However, there is no information on the effect of hydriding-dehydriding cycles on the hydriding properties of the V-Ti-based ternary alloys, especially the effective hydrogen content across the plateau, the slope of the plateau region and the pulverization resistance. Furthermore, there is controversy with regard to the hysteresis in the absorption-desorption plateau pressures for the V-Ti alloys. Lynch et al. [l] found that the hysteresis factor ln(P,/P,) is about 0.7 for the V-Ti-Fe alloys studied, independent of both iron and titanium contents. Ono et al. [5] observed that ln(P,/P,) for the V,,Ti,,, alloy is about 1.3. The present authors [6] have observed that V(5-ZOat.%Ti) binary alloys have a good pulverization resistance owing to their ductile nature, whereas they have a large hysteresis in the plateau pressure, ln(P,/
Pd) z 1.662.1,
which
could
be an inherent
result
of using
pure vanadium.
Elsevier Sequoia/Printed
in The Netherlands
65
The aim of the present study is to obtain more detailed information on the effect of the alloying elements on the hydriding properties of the V-Ti alloys and to examine the influence of absorptiondesorption cycles on their hydriding properties and pulverization resistance.
2. Experimental
details
The (V,_.Ti,),_,M,Y (x = 0.1-0.2; M =Al, Si, Zr, Cr, Fe, Co, Ni; y = 0.01-0.1) alloys were prepared by arc melting the pure metals under an argon atmosphere, the alloys being remelted several times for homogenization. Granular samples of about 0.2 mm diameter were machined from the ingot buttons for X-ray analysis and for measurement of the hydriding properties. Details of the experimental methods have been described elsewhere [6]. The X-ray diffraction profiles of all the alloys revealed a single b.c.c. phase. The cyclic hydriding was carried out on the alloys in the hydrogen pressure range between 1 MPa and 0.1 Pa at an appropriate temperature which ensured that the absorption -desorption plateau pressures were within the pressure range of the cycling process.
3. Results and discussion Some examples of the pressureecomposition desorption isotherms measured at 333 K for the (V,,,Ti,,,), _,,M, and (V,,,,Ti,,,,), _,M, alloys are shown in Fig. 1. It can be seen that the’alloying elements which contract the host lattice raise the plateau pressure, whereas the addition of zirconium, expanding the host lattice, decreases the pressure, although the addition of aluminium has the opposite effect. The maximum H/M values in the V,,,Ti,,, alloys with less than 2 at.% Zr and 5 at.% Cr are virtually the same as those alloys with less than 5 at.% Fe, i.e. H/M = 1.85. However, a for the V,,,,Ti,,, clear decrease in the maximum H/M was observed for the low titanium alloys containing 2 at.% Si and 5 at.% Ni, Al, Fe and for the high titanium alloys with 8 at.% Fe, 5 at.% Co, Ni, Cr and 10 at.% Cr, although the effective hydrogen content was A(H/M) z 0.6, except for the V,,,Ti,,,, alloy with 8 at.% Fe where A(H/M) = 0.3. Furthermore, the V,,Ti,,, alloy with 10 at.% Al did not form the p-dihydride in spite of the lattice-expanding element. Maeland et al. [4] have shown that there is a limitation to the alloying elements used to improve activation in group V metals: they should have atomic radii at least 5% smaller than those of the host metals. However, it was observed in the present study that the alloys with third elements such as zirconium and aluminium, which have larger atomic radii than those of the solvent metals, can react rapidly with hydrogen without activation treatment. The data on the effect of the alloying elements on the hydriding properties are summarized in Table 1. The following observations can be made. (1) The hydrogen absorption rate increases markedly with titanium
0.01~' ’ ’ ’ 0.8 0.6
’
1.0
Hydrogen
*
’
1.2
’
’
I.4
Content
’
’
1.6
’
I
1.8
I
J
2.0
(HIM)
Fig. 1. Pressure-composition desorption isotherms for (a) (V0.9Ti0.,),_,M, and WO.s,Ti,,,), -?My alloys measured at 333 K: (a) - - -, V,,,T4,,,; 0, (V,,,Ti,,),.,Cr,,; ~V~.~T~.,)~.~Ni~.~~; 17, tV~.~Ti~.~)~~Fe*.*~; 0, W0.9Tb.~ )o.&~o.oz; +, (V~.~Ti~,,)~.~S~.~~; W0,9Ti0., )o.9s&.0s: v, W0.9Ti0.1)0.J10., ; (b) - ~ -, Vo.ssTh; 0, (V,.,,Ti,,,,),,,,Cr~.OS;
(b) A, 8,
l3 W~.~‘%ddh.~; n t (Vo.~%,do d%.0~; A, (VO~sTi~.d~.~~C~~.~5~ 0, (Vo.,,Ti”.,5)0.95Feo.os; nS (V,.,,Ti,.,,),.,Fe,.,,.
content [6] and the rate is reduced by the addition of silicon and iron. (2) The enthalpy change )AHI for y-dihydride formation and decomposition decreases slightly by alloying with silicon, aluminium, iron, cobalt and nickel. The addition of chromium does not affect the AH value in the case of the low titanium alloy as zirconium does, but reduces it for the high titanium alloy. The entropy change (AS/ caused by the alloying is relatively small and there is a similar tendency in the enthaIpy change, (3) The hysteresis factor In(P,/P,) and the slope d(ln ~)/d(H/~), of the plateau pressure are slightly decreased by additions of iron, cobalt and nickel, although the effects are small in comparison with the increasing effect of titanium. The addition of chromium decreases the slope of the plateau but increases the hysteresis slightly. Thus improvement of the hysteresis in the V-Ti alloys cannot be
1
Alloy
-39 -40
-53 -38 -45 -52 -47 -43 -47
-43 -48
40 45 49 40 45 49 40 49 54 48 42 49 46 41 41 -136 -139
- 177 - 138 - 142 - 154 -160 -154 -111
- 148 -154
Abs.
Abs.
Des.
AS (J(molH,)-’
AH (kJ (mol Hz)-‘)
142 140 142 136 134 138 131 140 146 143 135 143 149 129 129
Des.
Km’)
1.8 2.0 1.5 1.9 1.9 2.3 1.8 1.7 1.9 1.7 1.7
1.6 1.6 1.6 0.2 0.5 0.8 0.7 0.6 0.6 0.4 1.1 1.3 0.8 1.0 1.3 3.1 1.4 1.5
d(lnP)/d(H/M)
of p-dihydride, hysteresis
h-Q, /Pd)
Effect of alloying elements on enthalpy and entropy changes for formation and dissociation hydrogen absorption rate of VTi-based alloys (sample weight, about 1.5 g)
TABLE
40 22 12 15 21 12 33 10 5 4 3 27 46 3 5
Time for 80% complete at 273 K (min)
factor, slope of plateau and
68
0) ( Vo.gT io.l)o.115Feo.os
0
1st
cycle
0 100th cycle A 300th cycle
0 1st
cycle
0 1OOthcycle A 300thcycle
0.6
0.8
1.0
1.2
Hydrogen
1.4
1.6
1.8
2.0
Content (HIM 1
Fig. 2. Pressure-composition isotherms measured (VO.sTiO.1)o.95Cro o5alloys after cyclic hydriding.
at 333 K for (a) (V,,sTi,,,)096Fe,~0,
and (b)
expected from addition of the third elements studied and the large hysteresis can be ascribed to the inherent nature of pure vanadium. For most hydrogen storage alloys, e.g. LaNi,, pulverization as a result of hydriding-dehydriding cycles is an unavoidable phenomenon leading to deterioration of the hydrogen absorption capacity. The pulverization resistance of the V-Ti-based alloys was examined by measurements of particle size distribution with hydriding cycles up to 300 cycles. The iron and chromiumbearing V-Ti alloys as well as the V,~,TiO,I binary alloy [6] showed no tendency to become finer powders even after 300 cycles. The pressure-composition isotherms measured at 333 K for the V,,,Ti,, alloys with 5 at.% Fe, Cr after cycling are shown in Fig. 2. The alloy with iron reveals a significant decrease in hydrogen storage capacity with increasing number of cycles, whereas the chromium-bearing alloy shows some reduction in the effective hydrogen content and also a tendency to increase the absorption-desorption plateau pressure with increasing number of cycles. Thus experience with the V,,Ti,,
69 1M
0.1 y 301
302
303
Lattice
304
305
306
Parameter
307
306
309
310
(pm!
Fig. 3. Relationship between decomposition plateau pressure and lattice parameter based alloys. (Numbers on the plot show atomic percentage of element M.)
for V Ti-
alloys containing chromium is favourable with respect to pulverization resistance and a relatively small loss of effective hydrogen content with increasing number of cycles. The stability of metal hydrides has been generally discussed in relation to the size of the interstices of the parent lattice. The decomposition plateau pressures of the VTi alloys are plotted against the lattice parameter in Fig. 3. There is a relatively good correlation in the plot except for the alloy with aluminium. As can be seen from Fig. 1, the alloys containing aluminium, iron, cobalt and nickel and also the V15 at.% Ti alloy with chromium reveal a big reduction in the maximum H/M value. Lynch et al. [7,8] have discussed the decline in hydrogen content observed in VTiiFe, VCr and TiiMo alloys in relation to a critical electron-to-atom (e/a) ratio and have indicated that there exists a critical value e/a = 5.1. The maximum H/M values measured at 273 K for the present V-Ti-based ternary alloys are plotted as a function of the e/a values in Fig. 4, together with the data for the vanadiumbased binary alloys [6,8] and Tii Mo alloys [8]. With the exception of the alloys with aluminium, a similar dependence of maximum hydrogen content on e/a ratio can be seen and the critical value appears to exist around e/a = 5.0 for the VTi-based alloys. Plots similar to those for the aluminiumcontaining alloys have been presented for TiiNb alloys containing germanium and silicon [9]. It should be noted that germanium and silicon as well as aluminium are non-transition elements. The above e/a ratio rule and the relationship between plateau pressure and lattice parameter give useful indications for the estimation of the
5
4
Electron-to-Atom
6 Ratio
Fig. 4. Relationship between maximum hydrogen content at 273 K and electron-to-atom vanadium-based binary and ternary alloys and Ti-Mo alloys.
ratio for
maximum hydrogen content and for control of the plateau pressure with alloying. However, application of these relations appears to be limited to alloys composed of transition metals.
References 1 J. F. Lynch,
2 3 4 5 6 7 8 9
G. G. A. S. Y. J. J. A.
A. J. Maeland and G. G. Libowitz, 2. Phys. Chem. N.F., 145 (1985) 51. G. Libowitz and A. J. Maeland, J. Less-Common Met., 131 (1987) 275. G. Libowitz and A. J. Maeland, Mater. Sci. Forum, 31 (1988) 177. J. Maeland, G. G. Libowitz, J. F. Lynch and G. Rak, J. Less-Common Met., 104 (1984) Ono, K. Nomura and Y. Ikeda, J. Less-Common Met., 72 (1980) 159. Sakamoto, A. Kagawa and E. Ono, to be published. F. Lynch, A. J. Maeland and G. G. Libowitz, 2. Phys. Chem. N.F., 145 (1985) 305. F. Lynch, J. J. Reilly and F. Millot, J. Phys. Chem. Solids, 39 (1978) 883. J. Maeland, G. G. Libowitz and J. F. Lynch, J. Less-Common Met., 104 (1984) 361.
133.
Journal
Absorption V-Ti-based A. Kagawa, Department
of the Less-Common
Metals, 172-174
(1991) 64-70
of hydrogen by vanadium-rich alloys E. Ono, T. Kusakabe
of Materials
Science
and Y. Sakamoto
and Engineering,
Nagasaki
University,
Nagasaki
852
(Japan)
Abstract The pressure-composition isotherms of dihydride formation in (Vi _ XTi,), by M, (X = 0.1-0.2; M = Al, Si, Zr, Cr, Fe, Co, Ni; y = 0.01-0.1) alloys were determined at temperatures between 273 and 433 K and hydrogen pressures up to 3 MPa. The effect of absorption-desorption cycles on the hydriding properties were also examined, together with an evaluation of the pulverization resistance. It was found from the experiment on hydriding cycles that the V,,Ti,,, alloys with chromium showed a good pulverization resistance and no significant deterioration of the effective hydrogen content, although the hysteresis factor was relatively large.
1. Introduction Dihydrides of vanadium-based b.c.c. solid solution alloys have been the subject of recent investigations because of their potential for use in metal hydride heat pumps and other similar applications [l-3]. Generally, the b.c.c. group V metals can be made to react rapidly with hydrogen at room temperature by alloying with a small amount of a second metal [4]. From a study of the monohydride (/?)edihydride (7) phase equilibrium for the vanadium-rich V-Ti-based alloys, Libowitz and coworkers [l, 31 have shown that the enthalpy and entropy changes for dihydride formation have relatively high values compared to those of LaNi, hydrides and that the alloys have flexibility in the choice of their thermodynamic properties through modification of the alloy composition. However, there is no information on the effect of hydriding-dehydriding cycles on the hydriding properties of the V-Ti-based ternary alloys, especially the effective hydrogen content across the plateau, the slope of the plateau region and the pulverization resistance. Furthermore, there is controversy with regard to the hysteresis in the absorption-desorption plateau pressures for the V-Ti alloys. Lynch et al. [l] found that the hysteresis factor ln(P,/P,) is about 0.7 for the V-Ti-Fe alloys studied, independent of both iron and titanium contents. Ono et al. [5] observed that ln(P,/P,) for the V,,Ti,,, alloy is about 1.3. The present authors [6] have observed that V(5-ZOat.%Ti) binary alloys have a good pulverization resistance owing to their ductile nature, whereas they have a large hysteresis in the plateau pressure, ln(P,/
Pd) z 1.662.1,
which
could
be an inherent
result
of using
pure vanadium.
Elsevier Sequoia/Printed
in The Netherlands
65
The aim of the present study is to obtain more detailed information on the effect of the alloying elements on the hydriding properties of the V-Ti alloys and to examine the influence of absorptiondesorption cycles on their hydriding properties and pulverization resistance.
2. Experimental
details
The (V,_.Ti,),_,M,Y (x = 0.1-0.2; M =Al, Si, Zr, Cr, Fe, Co, Ni; y = 0.01-0.1) alloys were prepared by arc melting the pure metals under an argon atmosphere, the alloys being remelted several times for homogenization. Granular samples of about 0.2 mm diameter were machined from the ingot buttons for X-ray analysis and for measurement of the hydriding properties. Details of the experimental methods have been described elsewhere [6]. The X-ray diffraction profiles of all the alloys revealed a single b.c.c. phase. The cyclic hydriding was carried out on the alloys in the hydrogen pressure range between 1 MPa and 0.1 Pa at an appropriate temperature which ensured that the absorption -desorption plateau pressures were within the pressure range of the cycling process.
3. Results and discussion Some examples of the pressureecomposition desorption isotherms measured at 333 K for the (V,,,Ti,,,), _,,M, and (V,,,,Ti,,,,), _,M, alloys are shown in Fig. 1. It can be seen that the’alloying elements which contract the host lattice raise the plateau pressure, whereas the addition of zirconium, expanding the host lattice, decreases the pressure, although the addition of aluminium has the opposite effect. The maximum H/M values in the V,,,Ti,,, alloys with less than 2 at.% Zr and 5 at.% Cr are virtually the same as those alloys with less than 5 at.% Fe, i.e. H/M = 1.85. However, a for the V,,,,Ti,,, clear decrease in the maximum H/M was observed for the low titanium alloys containing 2 at.% Si and 5 at.% Ni, Al, Fe and for the high titanium alloys with 8 at.% Fe, 5 at.% Co, Ni, Cr and 10 at.% Cr, although the effective hydrogen content was A(H/M) z 0.6, except for the V,,,Ti,,,, alloy with 8 at.% Fe where A(H/M) = 0.3. Furthermore, the V,,Ti,,, alloy with 10 at.% Al did not form the p-dihydride in spite of the lattice-expanding element. Maeland et al. [4] have shown that there is a limitation to the alloying elements used to improve activation in group V metals: they should have atomic radii at least 5% smaller than those of the host metals. However, it was observed in the present study that the alloys with third elements such as zirconium and aluminium, which have larger atomic radii than those of the solvent metals, can react rapidly with hydrogen without activation treatment. The data on the effect of the alloying elements on the hydriding properties are summarized in Table 1. The following observations can be made. (1) The hydrogen absorption rate increases markedly with titanium
0.01~' ’ ’ ’ 0.8 0.6
’
1.0
Hydrogen
*
’
1.2
’
’
I.4
Content
’
’
1.6
’
I
1.8
I
J
2.0
(HIM)
Fig. 1. Pressure-composition desorption isotherms for (a) (V0.9Ti0.,),_,M, and WO.s,Ti,,,), -?My alloys measured at 333 K: (a) - - -, V,,,T4,,,; 0, (V,,,Ti,,),.,Cr,,; ~V~.~T~.,)~.~Ni~.~~; 17, tV~.~Ti~.~)~~Fe*.*~; 0, W0.9Tb.~ )o.&~o.oz; +, (V~.~Ti~,,)~.~S~.~~; W0,9Ti0., )o.9s&.0s: v, W0.9Ti0.1)0.J10., ; (b) - ~ -, Vo.ssTh; 0, (V,.,,Ti,,,,),,,,Cr~.OS;
(b) A, 8,
l3 W~.~‘%ddh.~; n t (Vo.~%,do d%.0~; A, (VO~sTi~.d~.~~C~~.~5~ 0, (Vo.,,Ti”.,5)0.95Feo.os; nS (V,.,,Ti,.,,),.,Fe,.,,.
content [6] and the rate is reduced by the addition of silicon and iron. (2) The enthalpy change )AHI for y-dihydride formation and decomposition decreases slightly by alloying with silicon, aluminium, iron, cobalt and nickel. The addition of chromium does not affect the AH value in the case of the low titanium alloy as zirconium does, but reduces it for the high titanium alloy. The entropy change (AS/ caused by the alloying is relatively small and there is a similar tendency in the enthaIpy change, (3) The hysteresis factor In(P,/P,) and the slope d(ln ~)/d(H/~), of the plateau pressure are slightly decreased by additions of iron, cobalt and nickel, although the effects are small in comparison with the increasing effect of titanium. The addition of chromium decreases the slope of the plateau but increases the hysteresis slightly. Thus improvement of the hysteresis in the V-Ti alloys cannot be
1
Alloy
-39 -40
-53 -38 -45 -52 -47 -43 -47
-43 -48
40 45 49 40 45 49 40 49 54 48 42 49 46 41 41 -136 -139
- 177 - 138 - 142 - 154 -160 -154 -111
- 148 -154
Abs.
Abs.
Des.
AS (J(molH,)-’
AH (kJ (mol Hz)-‘)
142 140 142 136 134 138 131 140 146 143 135 143 149 129 129
Des.
Km’)
1.8 2.0 1.5 1.9 1.9 2.3 1.8 1.7 1.9 1.7 1.7
1.6 1.6 1.6 0.2 0.5 0.8 0.7 0.6 0.6 0.4 1.1 1.3 0.8 1.0 1.3 3.1 1.4 1.5
d(lnP)/d(H/M)
of p-dihydride, hysteresis
h-Q, /Pd)
Effect of alloying elements on enthalpy and entropy changes for formation and dissociation hydrogen absorption rate of VTi-based alloys (sample weight, about 1.5 g)
TABLE
40 22 12 15 21 12 33 10 5 4 3 27 46 3 5
Time for 80% complete at 273 K (min)
factor, slope of plateau and
68
0) ( Vo.gT io.l)o.115Feo.os
0
1st
cycle
0 100th cycle A 300th cycle
0 1st
cycle
0 1OOthcycle A 300thcycle
0.6
0.8
1.0
1.2
Hydrogen
1.4
1.6
1.8
2.0
Content (HIM 1
Fig. 2. Pressure-composition isotherms measured (VO.sTiO.1)o.95Cro o5alloys after cyclic hydriding.
at 333 K for (a) (V,,sTi,,,)096Fe,~0,
and (b)
expected from addition of the third elements studied and the large hysteresis can be ascribed to the inherent nature of pure vanadium. For most hydrogen storage alloys, e.g. LaNi,, pulverization as a result of hydriding-dehydriding cycles is an unavoidable phenomenon leading to deterioration of the hydrogen absorption capacity. The pulverization resistance of the V-Ti-based alloys was examined by measurements of particle size distribution with hydriding cycles up to 300 cycles. The iron and chromiumbearing V-Ti alloys as well as the V,~,TiO,I binary alloy [6] showed no tendency to become finer powders even after 300 cycles. The pressure-composition isotherms measured at 333 K for the V,,,Ti,, alloys with 5 at.% Fe, Cr after cycling are shown in Fig. 2. The alloy with iron reveals a significant decrease in hydrogen storage capacity with increasing number of cycles, whereas the chromium-bearing alloy shows some reduction in the effective hydrogen content and also a tendency to increase the absorption-desorption plateau pressure with increasing number of cycles. Thus experience with the V,,Ti,,
69 1M
0.1 y 301
302
303
Lattice
304
305
306
Parameter
307
306
309
310
(pm!
Fig. 3. Relationship between decomposition plateau pressure and lattice parameter based alloys. (Numbers on the plot show atomic percentage of element M.)
for V Ti-
alloys containing chromium is favourable with respect to pulverization resistance and a relatively small loss of effective hydrogen content with increasing number of cycles. The stability of metal hydrides has been generally discussed in relation to the size of the interstices of the parent lattice. The decomposition plateau pressures of the VTi alloys are plotted against the lattice parameter in Fig. 3. There is a relatively good correlation in the plot except for the alloy with aluminium. As can be seen from Fig. 1, the alloys containing aluminium, iron, cobalt and nickel and also the V15 at.% Ti alloy with chromium reveal a big reduction in the maximum H/M value. Lynch et al. [7,8] have discussed the decline in hydrogen content observed in VTiiFe, VCr and TiiMo alloys in relation to a critical electron-to-atom (e/a) ratio and have indicated that there exists a critical value e/a = 5.1. The maximum H/M values measured at 273 K for the present V-Ti-based ternary alloys are plotted as a function of the e/a values in Fig. 4, together with the data for the vanadiumbased binary alloys [6,8] and Tii Mo alloys [8]. With the exception of the alloys with aluminium, a similar dependence of maximum hydrogen content on e/a ratio can be seen and the critical value appears to exist around e/a = 5.0 for the VTi-based alloys. Plots similar to those for the aluminiumcontaining alloys have been presented for TiiNb alloys containing germanium and silicon [9]. It should be noted that germanium and silicon as well as aluminium are non-transition elements. The above e/a ratio rule and the relationship between plateau pressure and lattice parameter give useful indications for the estimation of the
5
4
Electron-to-Atom
6 Ratio
Fig. 4. Relationship between maximum hydrogen content at 273 K and electron-to-atom vanadium-based binary and ternary alloys and Ti-Mo alloys.
ratio for
maximum hydrogen content and for control of the plateau pressure with alloying. However, application of these relations appears to be limited to alloys composed of transition metals.
References 1 J. F. Lynch,
2 3 4 5 6 7 8 9
G. G. A. S. Y. J. J. A.
A. J. Maeland and G. G. Libowitz, 2. Phys. Chem. N.F., 145 (1985) 51. G. Libowitz and A. J. Maeland, J. Less-Common Met., 131 (1987) 275. G. Libowitz and A. J. Maeland, Mater. Sci. Forum, 31 (1988) 177. J. Maeland, G. G. Libowitz, J. F. Lynch and G. Rak, J. Less-Common Met., 104 (1984) Ono, K. Nomura and Y. Ikeda, J. Less-Common Met., 72 (1980) 159. Sakamoto, A. Kagawa and E. Ono, to be published. F. Lynch, A. J. Maeland and G. G. Libowitz, 2. Phys. Chem. N.F., 145 (1985) 305. F. Lynch, J. J. Reilly and F. Millot, J. Phys. Chem. Solids, 39 (1978) 883. J. Maeland, G. G. Libowitz and J. F. Lynch, J. Less-Common Met., 104 (1984) 361.
133.