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High pressure investigations on UO2 and UP
Journal of Nuclear Material 60 (1976) 339-340 0 North-Holland Publishing Company
LETTERS TO THE EDITORS - LETTRES AUX REDACTEURS
HIGH PRESSURE INVESTIGATIONS ON UO, AND UP S.N. VAIDYA, C. KARUNAKARAN
and M.D. KARKHANAVALA
Chemistry Division, Bhabha Atomic Research Centre Trombay, Bombay 400085,
India
and R. KRISHNAN Bhabha Atomic Research Centre Trombay, Bombay 40085,
India
Received 11 March 1976
Several rare earth compounds exhibit at high pressures, electronic and structural transformations which are generally associated with the electrons in the 4fshell [ 1,2]. In this context, it was felt that it would be worthwhile to examine whether similar transformations occur in actinide compounds also. This paper discusses the results of high pressure lattice parameter measurements on UO, and UP up to 180 Kb and resistance measurements on UO, up to 80 Kb. Uranium dioxide of near stoichiometric composition was prepeared by the reduction of nuclear pure U30, in hydrogen at 970 K for 2 hours. Uranium monophosphide was prepared by a two step reaction starting with UF4, Si and red phosphorous. The reaction product U3P4 was heated in vacuum at 1170 K to produce UP [3]. High pressure lattice parameters were determined using a diamond anvil camera [4]. The samples were in fine powder form. A silver foil was used as an internal pressure standard. MO K, radiation was used for this investigation. Lattice parameters of UOa and UP were determined from (11 l), (200), (220) and (3 11) lines. The (V/V-,) versus pressure curve deduced from these measurements is given in fig. 1. The isothermal bulk moduli obtained from these data are 4.8 + 0.1 Mb and 2.5 + 0.1 Mb for UO, and UP respectively. The adiabatic bulk modulus for UO, obtained from ultrasonic measurements [.5] is 4.7 * 0.04 Mb. Electrical resistance measurements were made with an opposed anvil apparatus, the details of which are given elsewhere [6,7]. Resistance specimens were in
the form of thin plates of dimensions 2.7 X 0.5 X 0.05 mm. Three different reei.stivity runs yielded reproducible values of relative resistance. Fig. 2 shows a typical plot of log R versus pressure for UO,. The resistance showed a drop by a factor of about 5 in 80 Kb. The present measurements yield a value of -10.9 X 1O-3 Kb-’ for d In R/dPat 40 Kb. The specific resistances of the pressed powder compacts obtained from these measurements were of the same order as the value quoted for single crystals of U02 at the ambient temperature. The behaviour of the high pressure resistivity of U02 is qualitatively similar to that of oxide semiconductors such as NiO, CuO, U,O, in this pressure range [S]. Anderson and Nafe [9] have attempted a correlation between isothermal bulk modulus and volume per
oal0
1
20
1
40
8
60
8
80 too PRESSUREKb
8
120
*
140
a
la
Fig. 1. V/Vu versus pressure -UOz and UP. 339
s
180
I
S.N.
340
Vaidya et al. /High
pressure investigations
on WI;? and UP
from the calculated values [l 11. Jayaraman et al. [l] have found pressure induced electronic transitions in SmTe, EuTe and YbTe which crystallize in the NaCl type structure. High pressure metallic phases in these rare earth compounds, as well as the ambient pressure temperature form of UP arise from the promotion of f-electrons to the conduction band. While the metallic phases of these rare earth chalcogenides transform to the CsCl type at high pressures, no such transformation has been found in UP up to about 180 Kbar.
4.2
Our tanks are due to Dr. S.R. Dharwadkar and Dr. J.P. Mittal for providing UO2 and UP for this investigati0.n. 0
10
20
30
40 50 PRESSURE
60
70
SO
Kb
Fig. 2. Log resistance versus pressure -UOz.
References [l ] A. Jayaraman, P.D. Demier and L.D. Longinotti, High
ion pair. They have shown that for compounds having a similar type of bonding, log BT versus log V should fall on a straight line of slope -4.0 in the case of oxides. If one uses this plot, then corresponding to an isothermal bulk modulus of 4.8 Mb for U02, the estimated volume per ion pair would be 9 cm3/mole, whereas it is calculated to be 16.4 cm3/mole. No explanation is put forward to explain this anomaly except to draw attention to the significant deviation from the Anderson-Nafe plot which is applicable to several oxides. UP is antiferromagnetic (TN = 120 K) and exhibits metallic conductivity at ambient temperature. The transition at the Neel temperature has been associated with the promotion of 5f electrons to the 6d-7s conduction band [lo]. Further simple models of ionic or metallic bonding do not apparently apply to UP, because .the observed lattice constant differs considerably
Temp. High Press. 7 (1975) 1. [2] A.K. Singh, A Jayaraman and A. Chatterjee, Solid State Commun. 9 (1971) 1459. [3] E. Ono, M. Kanno and T. Mukibo, J. Nucl. Sci. Tech. 8 (1971) 37. [4] W.A. Bassett, T. Takahashi and W.P. Stook, Rev. Sci. Instrum. 38 (1967) 37. [S] J.B. Wavhtman, MI. Wheat and H.J. Anderson, J. Nucl. Mater. 16 (1965) 42. [6] S.N. Vaidya, C. Karunakaran, A.S. Gokhale and M.D. Karkhanavala, BARC Report 803 (1975). [7] S.N. Vaidya, D.K. Joshi, and C. Karunakaran, to be published. [8] S. Minomura and H.G. Drickamer, J. Appl. Phys. 34 (1963) 3043. [9] O.L. Anderson and J.E. Nafe, J. Geophys. Res., 70 (1965) 3951. [lo] J.M. Robinson and P. Erdos, Phys. Rev. 8B (1973) 4333 [ 111 Compounds of interest in Nuclear Reactor Technology, eds. J.T. Waber and P. Chiotti, MetaIlurgical Society of AMIE (1964) 65,457.
LETTERS TO THE EDITORS - LETTRES AUX REDACTEURS
HIGH PRESSURE INVESTIGATIONS ON UO, AND UP S.N. VAIDYA, C. KARUNAKARAN
and M.D. KARKHANAVALA
Chemistry Division, Bhabha Atomic Research Centre Trombay, Bombay 400085,
India
and R. KRISHNAN Bhabha Atomic Research Centre Trombay, Bombay 40085,
India
Received 11 March 1976
Several rare earth compounds exhibit at high pressures, electronic and structural transformations which are generally associated with the electrons in the 4fshell [ 1,2]. In this context, it was felt that it would be worthwhile to examine whether similar transformations occur in actinide compounds also. This paper discusses the results of high pressure lattice parameter measurements on UO, and UP up to 180 Kb and resistance measurements on UO, up to 80 Kb. Uranium dioxide of near stoichiometric composition was prepeared by the reduction of nuclear pure U30, in hydrogen at 970 K for 2 hours. Uranium monophosphide was prepared by a two step reaction starting with UF4, Si and red phosphorous. The reaction product U3P4 was heated in vacuum at 1170 K to produce UP [3]. High pressure lattice parameters were determined using a diamond anvil camera [4]. The samples were in fine powder form. A silver foil was used as an internal pressure standard. MO K, radiation was used for this investigation. Lattice parameters of UOa and UP were determined from (11 l), (200), (220) and (3 11) lines. The (V/V-,) versus pressure curve deduced from these measurements is given in fig. 1. The isothermal bulk moduli obtained from these data are 4.8 + 0.1 Mb and 2.5 + 0.1 Mb for UO, and UP respectively. The adiabatic bulk modulus for UO, obtained from ultrasonic measurements [.5] is 4.7 * 0.04 Mb. Electrical resistance measurements were made with an opposed anvil apparatus, the details of which are given elsewhere [6,7]. Resistance specimens were in
the form of thin plates of dimensions 2.7 X 0.5 X 0.05 mm. Three different reei.stivity runs yielded reproducible values of relative resistance. Fig. 2 shows a typical plot of log R versus pressure for UO,. The resistance showed a drop by a factor of about 5 in 80 Kb. The present measurements yield a value of -10.9 X 1O-3 Kb-’ for d In R/dPat 40 Kb. The specific resistances of the pressed powder compacts obtained from these measurements were of the same order as the value quoted for single crystals of U02 at the ambient temperature. The behaviour of the high pressure resistivity of U02 is qualitatively similar to that of oxide semiconductors such as NiO, CuO, U,O, in this pressure range [S]. Anderson and Nafe [9] have attempted a correlation between isothermal bulk modulus and volume per
oal0
1
20
1
40
8
60
8
80 too PRESSUREKb
8
120
*
140
a
la
Fig. 1. V/Vu versus pressure -UOz and UP. 339
s
180
I
S.N.
340
Vaidya et al. /High
pressure investigations
on WI;? and UP
from the calculated values [l 11. Jayaraman et al. [l] have found pressure induced electronic transitions in SmTe, EuTe and YbTe which crystallize in the NaCl type structure. High pressure metallic phases in these rare earth compounds, as well as the ambient pressure temperature form of UP arise from the promotion of f-electrons to the conduction band. While the metallic phases of these rare earth chalcogenides transform to the CsCl type at high pressures, no such transformation has been found in UP up to about 180 Kbar.
4.2
Our tanks are due to Dr. S.R. Dharwadkar and Dr. J.P. Mittal for providing UO2 and UP for this investigati0.n. 0
10
20
30
40 50 PRESSURE
60
70
SO
Kb
Fig. 2. Log resistance versus pressure -UOz.
References [l ] A. Jayaraman, P.D. Demier and L.D. Longinotti, High
ion pair. They have shown that for compounds having a similar type of bonding, log BT versus log V should fall on a straight line of slope -4.0 in the case of oxides. If one uses this plot, then corresponding to an isothermal bulk modulus of 4.8 Mb for U02, the estimated volume per ion pair would be 9 cm3/mole, whereas it is calculated to be 16.4 cm3/mole. No explanation is put forward to explain this anomaly except to draw attention to the significant deviation from the Anderson-Nafe plot which is applicable to several oxides. UP is antiferromagnetic (TN = 120 K) and exhibits metallic conductivity at ambient temperature. The transition at the Neel temperature has been associated with the promotion of 5f electrons to the 6d-7s conduction band [lo]. Further simple models of ionic or metallic bonding do not apparently apply to UP, because .the observed lattice constant differs considerably
Temp. High Press. 7 (1975) 1. [2] A.K. Singh, A Jayaraman and A. Chatterjee, Solid State Commun. 9 (1971) 1459. [3] E. Ono, M. Kanno and T. Mukibo, J. Nucl. Sci. Tech. 8 (1971) 37. [4] W.A. Bassett, T. Takahashi and W.P. Stook, Rev. Sci. Instrum. 38 (1967) 37. [S] J.B. Wavhtman, MI. Wheat and H.J. Anderson, J. Nucl. Mater. 16 (1965) 42. [6] S.N. Vaidya, C. Karunakaran, A.S. Gokhale and M.D. Karkhanavala, BARC Report 803 (1975). [7] S.N. Vaidya, D.K. Joshi, and C. Karunakaran, to be published. [8] S. Minomura and H.G. Drickamer, J. Appl. Phys. 34 (1963) 3043. [9] O.L. Anderson and J.E. Nafe, J. Geophys. Res., 70 (1965) 3951. [lo] J.M. Robinson and P. Erdos, Phys. Rev. 8B (1973) 4333 [ 111 Compounds of interest in Nuclear Reactor Technology, eds. J.T. Waber and P. Chiotti, MetaIlurgical Society of AMIE (1964) 65,457.