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Pressure-induced orthorhombic-rhombohedral phase transition in NdNiO3
ELSEVIER
Physica B 234-236 (1997) 15-17
Pressure-induced orthorhombic-rhombohedral phase transition in NdNiO3 M. Medarde a'*, J. Mesot a, S. Rosenkranz", P. Lacorre u, W. Marshall c, S. Klotz a, J.S. Loveday c, G. Hamel d, S. Hull e, P. Radaelli f aLabor fdr Neutronenstreuung, ETH Ziirich & PSI, 5232 Villigen PSI, Switzerland bLaboratoire des Fluorures, Universit~ du Maine, 72017 Le Mans Cedex, France ~Department of Physics and Astronomy, University of Edinburgh, MayfieM road, Edinburgh EH9 3JZ, UK dUniversity Paris VI, 4 Place Jussieu, 75252 Paris Cedex 5, France eRutherford Appleton Laboratory, Chilton, Didcot, Oxon, 0 X l l OQX, UK flnstitut Laue Langevin, BP 156, 38042 Grenoble Cedex 9, France
Abstract
We report the first experimental observation of a pressure-induced structural phase transition in the RNiO3 series. At 40 kbar, the space group of NdNiO3 changes from Pbnm (orthorhombic) to the more symmetrical R3c (rhombohedral). This experiment confirms our previous results on PrNiO3 indicating that the symmetry of the structure increases with pressure.
Keywords: High pressure; Metal-insulator transition; Perovskite compounds RNiO3 perovskites (R = rare earth other than La) show a very sharp metal-insulator transition at a temperature TM_Ithat increases by decreasing the size of the rare-earth ion (see Fig. 1). Thus, whereas LaNiO3 remains metallic, Tu_! is 130, 200, 400 and 480 K for R = Pr, Nd, Sm and Eu, respectively [1]. It is also noteworthy that, at room temperature, metallic LaNiO3 has rhombohedral symmetry while for the other R ions the symmetry is orthorhombic (Fig. 1). Resistivity measurements under high pressure (up to 15 kbar) have been reported for some members of the series (R = Pr, Nd and Lc,o.3 Ndo.7) [2, 3]. The most interesting results of these experiments can be summarised as follows: first, TM~ decreases with pressure (the metallic state is favoured); second, ~TM-l/~P shows an unusually high value ( - 4 . 2 K/kbar from Ref. [2],
* Corresponding author. 0921-4526/97/$17.00 © •997 Elsevier Science B.V. All rights reserved Pl! S 0 9 2 1 - 4 5 2 6 ( 9 6 ) 0 0 8 6 2 - 9
Sm '
Eu 1200
Nd Pr La ' \ ' cubic' ~ Pm3m 1
1000
orth~brh2mbi~rhombO. c hcedral
~, 800 600 Q..
I-- 400 200
~,
metallic~ R
in~sulla"~,~ tor ~rrom.ag.netic..,~,,...~,, 1.078 1.096 1.114 1.132 1.150 R ionicradius(A) Fig. 1. Phase diagram of RNiO3.
16
M. Medarde et al. /Physica B 234-236 (1997) 15 17
- 7 . 6 K/kbar from Ref. [3]; third, ~TM_,/~Pis the same for all studied nickelates. The last feature seems to indicate that a common structural and/or electronic parameter is controlI
I
ling the evolution of the TM_I with pressure. The first neutron diffraction experiments performed at relatively low pressures on PrNiO3 (up to 5 kbar) indicated that a small diminution of the N i - O
I
I
I
I
+
NdNiO3 25 kbar Pbnm
O
,4
t/3 O +
÷
O O
t~ O
/
I
I 0.5
I 1.0
I 1.5
I 2.0
I 2.5
I 3.0
d spacing (A)
(a) 1
I
I
I
I
NdNiO3 60 kbar R3c
t.t3 o
I
A
O o
tt3 O
~
v
'
~
'
~""
TM-"
'y ~ vw','~'r,I illllll.~,Irt
t
I 0.5
(b)
I 1.0
I Z.5
I 2.0
I 2.5
d spacing (A) Fig. 2. Observed and calculated patterns of NdNiO3 at 25 and 60 kbar.
I 3.0
17
M. Medarde et al. / Physica B 234-236 (1997) 15-17
distance dNi_o and a simultaneous increase of the N i - O - N i superexchange angle 0 occurs under hydrostatic pressure [4, 5]. A less distorted structure would be then stabilised by applying external pressure. This curious behaviour is in strong disagreement with the pressure evolution of the superexchange angle observed in other isostructural perovskite systems. Several investigations on (Fel _ xMgx)SiO3 [6] and N a M n F 3 [7] clearly indicate that in these compounds 0 decreases with pressure. In order to confirm our previous results, we have performed a series of high-pressure neutron powder diffraction experiments at P O L A R I S (ISIS) by using the Paris-Edinburgh cell. The nickelate studied in this case was NdNiO3. D a t a were collected using tungsten carbide anvils over a pressure range between 15 and 85 kbar as determined from the previously determined equation of state. As a result of careful shielding, the collected spectra were free from contamination. To get reliable Bragg intensities the spectra were corrected for attenuation due to the pressure cell and the background was subtracted. The Rietveld refinements of the patterns recorded at 25 and 6 0 k b a r are displayed in Fig. 2. The values of 0 derived from the refinements are summarised in Fig. 3. Note that, in spite of the large error bars, these results clearly show that the superexchange angle increases with pressure. O u r former low-pressure results [4] are then fully confirmed. More impressive is the observation of a phase transition from orthorhombic to rhombohedral symmetry at about 40 kbar. The evolution of the structure under external pressure is then qualitatively similar to those observed by substituting the rare-earth ion by another with larger ionic radius (chemical pressure)• In both the cases, a less-distorted perovskite framework, together with
161 Pbnm
160 A
o)
159
(9 -o 158 ¢D 157 156 0
t
R-3C
i i 1
!
20
1
.
.
40
60
80
100
Pressure [kbar] Fig. 3. Pressure dependence of the Ni-O-Ni superexchange angle 0.
enhanced metallic conductivity is progressively reached. A detailed quantitative study of the differences between these two mechanisms is currently in progress•
References
[1] P. Lacorre, J.B. Torrance, J. Pannetier, A•I. Nazzal, P.W. Wang and T.C. Huang, J. Solid State Chem. 91 (1991) 225. [2] X. Obradors, L.M. Paulius, M.B. Maple, J.B. Torrance, A.I. Nazzal, J. Fontcuberta and X. Granados, Phys. Rev. B 47 (1993) 12 353. [3] P.C. Canfield, J.D• Thompson, S.W. Cheong and L.W. Rupp, Phys. Rev. B 47 (1993) 12357. [4] M. Medarde, J. Mesot, P. Lacorre, S. Rosenkranz, P. Fischer and K. Gobrecht, Phys. Rev. B 52 (1995) 9248; J. Mesot, M. Medarde, S. Rosenkranz, P. Fischer, P. Lacorre and K. Gobrecht, High Press. Res. 14 (1995) 35. [5] M. Medarde et al., in preparation. [6] H.K. Mao, R.J. Hemley, Y. Fei, J.F. Shu, L.C. Chen, A.P. Jephcoat and Y. Wu, J. Geophys. Res. 96 (1991) 8069. [7] A. Katrusiak and A. Ratuszna, Solid State Commun. 84 (1992) 435.
Physica B 234-236 (1997) 15-17
Pressure-induced orthorhombic-rhombohedral phase transition in NdNiO3 M. Medarde a'*, J. Mesot a, S. Rosenkranz", P. Lacorre u, W. Marshall c, S. Klotz a, J.S. Loveday c, G. Hamel d, S. Hull e, P. Radaelli f aLabor fdr Neutronenstreuung, ETH Ziirich & PSI, 5232 Villigen PSI, Switzerland bLaboratoire des Fluorures, Universit~ du Maine, 72017 Le Mans Cedex, France ~Department of Physics and Astronomy, University of Edinburgh, MayfieM road, Edinburgh EH9 3JZ, UK dUniversity Paris VI, 4 Place Jussieu, 75252 Paris Cedex 5, France eRutherford Appleton Laboratory, Chilton, Didcot, Oxon, 0 X l l OQX, UK flnstitut Laue Langevin, BP 156, 38042 Grenoble Cedex 9, France
Abstract
We report the first experimental observation of a pressure-induced structural phase transition in the RNiO3 series. At 40 kbar, the space group of NdNiO3 changes from Pbnm (orthorhombic) to the more symmetrical R3c (rhombohedral). This experiment confirms our previous results on PrNiO3 indicating that the symmetry of the structure increases with pressure.
Keywords: High pressure; Metal-insulator transition; Perovskite compounds RNiO3 perovskites (R = rare earth other than La) show a very sharp metal-insulator transition at a temperature TM_Ithat increases by decreasing the size of the rare-earth ion (see Fig. 1). Thus, whereas LaNiO3 remains metallic, Tu_! is 130, 200, 400 and 480 K for R = Pr, Nd, Sm and Eu, respectively [1]. It is also noteworthy that, at room temperature, metallic LaNiO3 has rhombohedral symmetry while for the other R ions the symmetry is orthorhombic (Fig. 1). Resistivity measurements under high pressure (up to 15 kbar) have been reported for some members of the series (R = Pr, Nd and Lc,o.3 Ndo.7) [2, 3]. The most interesting results of these experiments can be summarised as follows: first, TM~ decreases with pressure (the metallic state is favoured); second, ~TM-l/~P shows an unusually high value ( - 4 . 2 K/kbar from Ref. [2],
* Corresponding author. 0921-4526/97/$17.00 © •997 Elsevier Science B.V. All rights reserved Pl! S 0 9 2 1 - 4 5 2 6 ( 9 6 ) 0 0 8 6 2 - 9
Sm '
Eu 1200
Nd Pr La ' \ ' cubic' ~ Pm3m 1
1000
orth~brh2mbi~rhombO. c hcedral
~, 800 600 Q..
I-- 400 200
~,
metallic~ R
in~sulla"~,~ tor ~rrom.ag.netic..,~,,...~,, 1.078 1.096 1.114 1.132 1.150 R ionicradius(A) Fig. 1. Phase diagram of RNiO3.
16
M. Medarde et al. /Physica B 234-236 (1997) 15 17
- 7 . 6 K/kbar from Ref. [3]; third, ~TM_,/~Pis the same for all studied nickelates. The last feature seems to indicate that a common structural and/or electronic parameter is controlI
I
ling the evolution of the TM_I with pressure. The first neutron diffraction experiments performed at relatively low pressures on PrNiO3 (up to 5 kbar) indicated that a small diminution of the N i - O
I
I
I
I
+
NdNiO3 25 kbar Pbnm
O
,4
t/3 O +
÷
O O
t~ O
/
I
I 0.5
I 1.0
I 1.5
I 2.0
I 2.5
I 3.0
d spacing (A)
(a) 1
I
I
I
I
NdNiO3 60 kbar R3c
t.t3 o
I
A
O o
tt3 O
~
v
'
~
'
~""
TM-"
'y ~ vw','~'r,I illllll.~,Irt
t
I 0.5
(b)
I 1.0
I Z.5
I 2.0
I 2.5
d spacing (A) Fig. 2. Observed and calculated patterns of NdNiO3 at 25 and 60 kbar.
I 3.0
17
M. Medarde et al. / Physica B 234-236 (1997) 15-17
distance dNi_o and a simultaneous increase of the N i - O - N i superexchange angle 0 occurs under hydrostatic pressure [4, 5]. A less distorted structure would be then stabilised by applying external pressure. This curious behaviour is in strong disagreement with the pressure evolution of the superexchange angle observed in other isostructural perovskite systems. Several investigations on (Fel _ xMgx)SiO3 [6] and N a M n F 3 [7] clearly indicate that in these compounds 0 decreases with pressure. In order to confirm our previous results, we have performed a series of high-pressure neutron powder diffraction experiments at P O L A R I S (ISIS) by using the Paris-Edinburgh cell. The nickelate studied in this case was NdNiO3. D a t a were collected using tungsten carbide anvils over a pressure range between 15 and 85 kbar as determined from the previously determined equation of state. As a result of careful shielding, the collected spectra were free from contamination. To get reliable Bragg intensities the spectra were corrected for attenuation due to the pressure cell and the background was subtracted. The Rietveld refinements of the patterns recorded at 25 and 6 0 k b a r are displayed in Fig. 2. The values of 0 derived from the refinements are summarised in Fig. 3. Note that, in spite of the large error bars, these results clearly show that the superexchange angle increases with pressure. O u r former low-pressure results [4] are then fully confirmed. More impressive is the observation of a phase transition from orthorhombic to rhombohedral symmetry at about 40 kbar. The evolution of the structure under external pressure is then qualitatively similar to those observed by substituting the rare-earth ion by another with larger ionic radius (chemical pressure)• In both the cases, a less-distorted perovskite framework, together with
161 Pbnm
160 A
o)
159
(9 -o 158 ¢D 157 156 0
t
R-3C
i i 1
!
20
1
.
.
40
60
80
100
Pressure [kbar] Fig. 3. Pressure dependence of the Ni-O-Ni superexchange angle 0.
enhanced metallic conductivity is progressively reached. A detailed quantitative study of the differences between these two mechanisms is currently in progress•
References
[1] P. Lacorre, J.B. Torrance, J. Pannetier, A•I. Nazzal, P.W. Wang and T.C. Huang, J. Solid State Chem. 91 (1991) 225. [2] X. Obradors, L.M. Paulius, M.B. Maple, J.B. Torrance, A.I. Nazzal, J. Fontcuberta and X. Granados, Phys. Rev. B 47 (1993) 12 353. [3] P.C. Canfield, J.D• Thompson, S.W. Cheong and L.W. Rupp, Phys. Rev. B 47 (1993) 12357. [4] M. Medarde, J. Mesot, P. Lacorre, S. Rosenkranz, P. Fischer and K. Gobrecht, Phys. Rev. B 52 (1995) 9248; J. Mesot, M. Medarde, S. Rosenkranz, P. Fischer, P. Lacorre and K. Gobrecht, High Press. Res. 14 (1995) 35. [5] M. Medarde et al., in preparation. [6] H.K. Mao, R.J. Hemley, Y. Fei, J.F. Shu, L.C. Chen, A.P. Jephcoat and Y. Wu, J. Geophys. Res. 96 (1991) 8069. [7] A. Katrusiak and A. Ratuszna, Solid State Commun. 84 (1992) 435.