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Compressibility of Ni3In
Physica 139 & 140B (1986) North-Holland, Amsterdam
311-313
COMPRESSIBILITY
OF N&In
A.W. WEBB and E.F. SKELTON US Naval Research Laboratory, Washington, DC 20375-SfX?O, USA S.B. QADRI SachslFreeman
J.F.
Associates,
Bowie, MD 20715,
USA
CANNON
Brigham
Young University, Provo,
UT 84602, USA
Ni,Sn and several isomorphs including Ni,In, share a hexagonal structure, and transform to a cubic structure at high pressures and high temperatures HP HT. The HP HT polymorph has a larger volume for several of these compounds. HP X-ray diffraction studies found the compressibility of cubic Ni,In to be 44% greater than the normal form, which explains in part the origin of the volume anomaly.
while at pressures of 6.5 GPa. Details of these syntheses have been given elsewhere [3,4].
1. Introduction Under normal pressure and temperature, each of the compounds Fe,.%, Ni,Sn, Ti,Sn, N&In and Sc,In crystallizes in a hexagonal, layered structure of the Mg,Cd-type (DO,,) [ 1,2]. Recent studies at elevated pressures and temperatures (HP HT) have shown each of these compounds to be polymorphic [3]. The resultant cubic Cu,Autype (Ll,) structure temperature has a lower X-ray density than the starting materials in every case except for Sc,In. The structures both consist of ordered close-packed layers stacked either in hexagonal ACACAC . . . or cubic ABCABC . . . order, and related by a glide of V3/3a. The relative compressibilities and thermal expansivities of these two structures were investigated for Ni,In seeking a reason for this anomalous behaviour.
3. Experimental
techniques
In order to minimize the time required to study the compressibility of the two polymorphs of Ni,In, advantage was taken of the extremely intense X-radiation available from the synchrotron at Stanford Synchrotron Radiation Laboratory (SSRL). Techniques have been developed over the past several years for the study of materials using diamond anvil cells at both elevated pressures and temperatures using this facility [5,6]. NaCl was used as an internal pressure calibrant, using the Decker equation of state [7]. Subsequent film study of the ambient polymorph was also undertaken with a diamond anvil cell of the Mao-Bell design, [8] with exposures typically of 150 h using MO Km radiation.
2. Materials The hexagonal Ni,In was formed from the elements by arc melting. The cubic material was formed by subjecting the hexagonal material to a temperature of SOO-1200°C for periods of 15-20 h 037%4363/86/$03.50 0 (North-Holland Physics
Elsevier Science Publishers Publishing Division)
4. Results A series of ten runs was made with a total of 98 data points at ambient temperature and another B.V.
A. W. Webb et al. I Compressibility of Ni,ln
312
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PRESSURE
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Fig. 2
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A.W.
Webb et al.
16 at elevated temperatures. Only the ambient data are considered hereafter, as the data currently available are insufficient for an understanding of the elevated temperature regime. The compressibility of the HP cubic Ni,In phase is found to be essentially linear to nearly 6 GPa (fig. 1). The data points were fit to a linear equation (given by the solid line), V/V, = 1 -0.007052P
(GPa) ,
with a standard deviation of 0.0577 (shown by the bar). The scatter in the data is unusually large compared to similar measurements on other samples, and is attributed in part to the nature of sample, and in part of positioning variations with the cell during a run. The compressibility of hexagonal Ni,In is compared to that of the cubic polymorph in fig. 2. The dashed line is the fit for the cubic polymorph’s relative volume, while the open data points give values for the hexagonal form obtained at SSRL and the filled data points were derived from the film work, taken to extend the pressure limits of the study. The solid line is the fit to the hexagonal data, V/V,, = 1 - 0.00491OP
(GPa)
,
with a standard deviation of 0.00449. The uncertainties are given by the bars. As the hexagonal form is less compressible than the HP HT polymorph, there should be some pressure P, at which the volumes are equal. The ambient volumes are 52.10 (hexagonal) and 53.03 (cubic) cc/formula unit, which, combined with the compressibilities yields a value at ambient
I CCompressibility of Ni,In
313
temperature of P, = 10.3 GPa. The thermal expansivities are not currently known, either at ambient or elevated pressures, so that the effects of temperature on volumes cannot yet be estimated. The fact that the conversion is so sluggish for systems with an ambient -AV, but rapid for Sc,In for which AV is positive suggests that the conditions used are near equilibrium for the two structures. Since the observed reaction pressure is well below PT estimated above, strong thermal effects must also be involved, i.e., the thermal expansion of the hexagonal form would have to exceed that of the cubic polymorph. Another possibility is that at synthesis conditions a third structure is formed which subsequently transforms to the recovered phase. However, no transformation was noted in either the hexagonal or cubic forms at ambient temperature in the X-ray diffraction studies. Both the possibility of such a HP HT polymorphism and the lack of thermal expansivities suggest the need for further study.
References [l] W.B. Pearson, Handbook of Lattice Spacings and Structures of Metals and Alloys (Pergamon, New York, 1958). [2] V.B. Compton and B.T. Matthias, Acta Cryst. 15 (1962) 94. [3] J.F. Cannon, Mat. Res. Sot. Symp. Proc. 22 (1984) 113. [4] J.F. Cannon and H.T. Hall, J. Less-Common Metals 40 (1975) 313. [S] E.F. Skelton, J.P. Kirkland and S.B. Qadri, J. Appl. Crystallogr. 15 (1982) 82. [6] E.F. Skelton, S.B. Qadri. A.W. Webb, C.W. Lee and J.P. Kirkland, Rev. Sci. Instr. 54 (1983) 403. [7] D.L. Decker, J. Appl. Phys. 42 (1971) 3239. [8] H.K. Mao and P.M. Bell, Carnegie Inst. Washington, Year Book 77 (1978) 904.
311-313
COMPRESSIBILITY
OF N&In
A.W. WEBB and E.F. SKELTON US Naval Research Laboratory, Washington, DC 20375-SfX?O, USA S.B. QADRI SachslFreeman
J.F.
Associates,
Bowie, MD 20715,
USA
CANNON
Brigham
Young University, Provo,
UT 84602, USA
Ni,Sn and several isomorphs including Ni,In, share a hexagonal structure, and transform to a cubic structure at high pressures and high temperatures HP HT. The HP HT polymorph has a larger volume for several of these compounds. HP X-ray diffraction studies found the compressibility of cubic Ni,In to be 44% greater than the normal form, which explains in part the origin of the volume anomaly.
while at pressures of 6.5 GPa. Details of these syntheses have been given elsewhere [3,4].
1. Introduction Under normal pressure and temperature, each of the compounds Fe,.%, Ni,Sn, Ti,Sn, N&In and Sc,In crystallizes in a hexagonal, layered structure of the Mg,Cd-type (DO,,) [ 1,2]. Recent studies at elevated pressures and temperatures (HP HT) have shown each of these compounds to be polymorphic [3]. The resultant cubic Cu,Autype (Ll,) structure temperature has a lower X-ray density than the starting materials in every case except for Sc,In. The structures both consist of ordered close-packed layers stacked either in hexagonal ACACAC . . . or cubic ABCABC . . . order, and related by a glide of V3/3a. The relative compressibilities and thermal expansivities of these two structures were investigated for Ni,In seeking a reason for this anomalous behaviour.
3. Experimental
techniques
In order to minimize the time required to study the compressibility of the two polymorphs of Ni,In, advantage was taken of the extremely intense X-radiation available from the synchrotron at Stanford Synchrotron Radiation Laboratory (SSRL). Techniques have been developed over the past several years for the study of materials using diamond anvil cells at both elevated pressures and temperatures using this facility [5,6]. NaCl was used as an internal pressure calibrant, using the Decker equation of state [7]. Subsequent film study of the ambient polymorph was also undertaken with a diamond anvil cell of the Mao-Bell design, [8] with exposures typically of 150 h using MO Km radiation.
2. Materials The hexagonal Ni,In was formed from the elements by arc melting. The cubic material was formed by subjecting the hexagonal material to a temperature of SOO-1200°C for periods of 15-20 h 037%4363/86/$03.50 0 (North-Holland Physics
Elsevier Science Publishers Publishing Division)
4. Results A series of ten runs was made with a total of 98 data points at ambient temperature and another B.V.
A. W. Webb et al. I Compressibility of Ni,ln
312
\
60** 0
0
0
0
0
,995;
0
O 79 0 0
O0 0 000 0 @ 0
0
0
0 0
0
0
0 Oo \ 8 0 0
0 Qo .990-
0
0 0
‘A
1,
0
%I
0
I
I
I
I
I
I
0
I
2
3
4
5
I
I
PRESSURE
L 6
(GPo)
Fig. 1
1.000
‘,
\
.980-
+
\_
\
-\ \
\
0
\ \
‘\
‘,
\
\
‘xx_
-, ’
\
l_
0 \
\
I
I
0
. \
.970.9602
3 PRESSURE
Fig. 2
(GPo)
\-1 ,
\
\
I
I
4
5
-_
6
A.W.
Webb et al.
16 at elevated temperatures. Only the ambient data are considered hereafter, as the data currently available are insufficient for an understanding of the elevated temperature regime. The compressibility of the HP cubic Ni,In phase is found to be essentially linear to nearly 6 GPa (fig. 1). The data points were fit to a linear equation (given by the solid line), V/V, = 1 -0.007052P
(GPa) ,
with a standard deviation of 0.0577 (shown by the bar). The scatter in the data is unusually large compared to similar measurements on other samples, and is attributed in part to the nature of sample, and in part of positioning variations with the cell during a run. The compressibility of hexagonal Ni,In is compared to that of the cubic polymorph in fig. 2. The dashed line is the fit for the cubic polymorph’s relative volume, while the open data points give values for the hexagonal form obtained at SSRL and the filled data points were derived from the film work, taken to extend the pressure limits of the study. The solid line is the fit to the hexagonal data, V/V,, = 1 - 0.00491OP
(GPa)
,
with a standard deviation of 0.00449. The uncertainties are given by the bars. As the hexagonal form is less compressible than the HP HT polymorph, there should be some pressure P, at which the volumes are equal. The ambient volumes are 52.10 (hexagonal) and 53.03 (cubic) cc/formula unit, which, combined with the compressibilities yields a value at ambient
I CCompressibility of Ni,In
313
temperature of P, = 10.3 GPa. The thermal expansivities are not currently known, either at ambient or elevated pressures, so that the effects of temperature on volumes cannot yet be estimated. The fact that the conversion is so sluggish for systems with an ambient -AV, but rapid for Sc,In for which AV is positive suggests that the conditions used are near equilibrium for the two structures. Since the observed reaction pressure is well below PT estimated above, strong thermal effects must also be involved, i.e., the thermal expansion of the hexagonal form would have to exceed that of the cubic polymorph. Another possibility is that at synthesis conditions a third structure is formed which subsequently transforms to the recovered phase. However, no transformation was noted in either the hexagonal or cubic forms at ambient temperature in the X-ray diffraction studies. Both the possibility of such a HP HT polymorphism and the lack of thermal expansivities suggest the need for further study.
References [l] W.B. Pearson, Handbook of Lattice Spacings and Structures of Metals and Alloys (Pergamon, New York, 1958). [2] V.B. Compton and B.T. Matthias, Acta Cryst. 15 (1962) 94. [3] J.F. Cannon, Mat. Res. Sot. Symp. Proc. 22 (1984) 113. [4] J.F. Cannon and H.T. Hall, J. Less-Common Metals 40 (1975) 313. [S] E.F. Skelton, J.P. Kirkland and S.B. Qadri, J. Appl. Crystallogr. 15 (1982) 82. [6] E.F. Skelton, S.B. Qadri. A.W. Webb, C.W. Lee and J.P. Kirkland, Rev. Sci. Instr. 54 (1983) 403. [7] D.L. Decker, J. Appl. Phys. 42 (1971) 3239. [8] H.K. Mao and P.M. Bell, Carnegie Inst. Washington, Year Book 77 (1978) 904.