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Phase diagram of ReO3 in the vicinity of the “compressibility collapse” transition
Materials Science and Engineering, 49 (1981) P7 -P10
P7
Phase Diagram of ReO3 in the Vicinity of the "Compressibility Collapse" Transition J. E. SCHIRBER, L. J. A Z E V E D O ,
A. N A R A T H
and B. M O R O S I N
Sandia National Laboratories, Albuquerque, N M 87185 (U.S.A.) (Received February 9, 1981)
SUMMARY
The temperature-pressure phase diagram delineating the "compressibility collapse" transition in the metallic perovskite-structured compound Re03 was determined between 1 and 300 K by a combination o f de Haasvan Alphen and nuclear magnetic resonance measurements as a function o f pressure. The high pressure phase is thought to have a structure with the space group Ira3; this has not yet been verified directly but it is consistent with an increasing amount o f indirect evidence.
1. INTRODUCTION
We have recently [1] identified a novel second-order phase transition in the metallic perovskite-structured compound ReO3. The most unusual property of this transition is that the high pressure phase has a much larger (by a factor of about 7) compressibility than the normal volume phase, giving rise to its designation as the "compressibility collapse" transition. In this paper we present our determination of the temperature- pressure phase boundary which separates the normal volume and the high pressure modifications.
2. EXPERIMENTAL PROCEDURE
The samples were single crystals of roughly millimeter dimensions grown [2] in iodine vapour. The chemical purity of the starting material was determined to be greater than 99.99q% by spectroscopic analysis. These single crystals were of high perfection, as indicated by the electronic mean free paths. Extremely large q u a n t u m oscillations were observed with measured Dingle temperatures 0025-541618110000-00001502.50
(determined from the amplitudes of the de Haas-van Alphen (dHvA) oscillations) which were typically in the temperature range of a few tenths of a kelvin. For the nuclear magnetic resonance (NMR) experiments that we shah discuss, these crystals were powdered so that they passed through a 325 mesh screen. The phase transition was detected (1) by the change in slope of the dHvA crosssectional area with pressure at low temperatures [1], (2) by observation of the change in amplitude of the NMR signal of the lSTRe nucleus due to the onset of first-order quadrupolar effects [3] and (3) by measurements of the lattice constant as a function of pressure at room temperature [1]. The first two techniques were by far the most accurate for determining the phase diagram.
3. RESULTS AND DISCUSSION
A derivative method for measurement of the pressure dependence of the Fermi surface has been developed in which the position in field of a single dHvA oscillation is monitored at pressures of several kilobars [1]. The slope of this position in field or phase is a direct measure of the pressure derivative of the cross section. The pressure is conveniently varied and generated by careful isobaric freezing [4] of helium. In Fig. 1 such a plot for a prominent set of oscillations arising from the a sheet [1] of the Fermi surface is shown. A very sharp break at 2.45 kbar is obsewed, which corresponds to a discontinuous j u m p in the compressibility of ReO3. The data shown comprise four separate excursions through the transition. No sign of hysteresis was observed and the volume change associated with the transition is esti© Elsevier Sequoia/Printed in The Netherlands
P8 I
I
I
61
I
./
/ 32 x I0"4 k b o r ' ~
'/
4w
/ /
00-""%'
5--
II
'
21
Pressure
e
I
,
3
i
,
I
4
(kbar)
Fig. 1. The shift in phase vs. pressure for the ~ frequency of the Fermi suface of ReO 3 for B//[110] at 100 kG. I,(30 - .
We have exploited t he quadrupolar effects on t he lSTRe NMR t o show t hat t h e symm e t r y at t he rheni um site is less t han cubic above t he transition [3]. T he di m i nut i on o f t he amplitude o f t he resonance when t h e 2I (where ! denot es t he t o t a l nuclear spin) first-order satellites move away f r o m t he central ~1 ~_. _ 1-~ line serves as a sensitive indicator o f the onset o f t he transition. The predicted amplitude ratio is 35:9, assuming t h a t all five transitions are observed for the lSVRe nucleus with I --~.5 Figure 3 shows a plot o f such data at 76 K. In Fig. 4 we show t he phase diagram in t h e t e m p e r a t u r e - p r e s s u r e plane for t he compressibility collapse transition det erm i ned using our NMR and dHvA data. We summarize these data in Table 1 t o g e t h e r with t h e uncertainties involved in each det erm i nat i on o f t h e transition.
.9! l-
c
14
>_ 12
~.98
lID
3.9~ l .96
a: >.
8 6
~
4
\i ½ !
_z 2I
½
0:
.95
40 Pressure
3 PRESSURE (kbar)
z
I
210
60 (kbor)
SIC)
I00
Fig. 2. Reduced lattice constant v s . pressure for ReO 3 at room temperature: -- -- --, an extension of the data for pressures below 4 kbar.
mated t o be less t ha n 2 parts in 10 5 (based o n th e sensitivity o f t he phase shift t echni que in this experiment). We cite these factors as evidence t h a t t h e transition is second order in nature. We have verified this j u m p in compressibility b y direct measurements [1] o f t he lattice constant as a f u n c t i o n o f pressure. Our data are shown in Fig. 2. The low pressure slope d eter min ed hydrostatically f r om b o t h p o w d e r studies and single-crystal Weissenberg X-ray studies is shown as a b r o k e n line. Although this clearly shows a large increase in compressibility in t he high pressure state, t h e accuracy o f t he pressure calibration (via a silver internal standard) in t h e d i a m o n d anvil cell is t o o low to d e t e r m i n e t h e phase boundary.
4
Fig. 3. Amplitude (arbitrary units) of the lS7Re nuclear magnetic resonance vs. pressure for ReO 3 at 75 K and a frequency of 10 MHz: . . . . , the theoretically predicted diminution of the amplitude. The vertical arrow is our definition of the transition. i
300
J
I
,.~/
'
I
(
200
~
~-
~/~
½ I00
J
/ 0
2
i/
I
3
,
I
4
PRESSURE:
,
I
5
I
i
6
(kbor)
Fig. 4. Temperature-pressure dependence of the compressibility collapse transition in ReO s. The
full curve is shown only as a guide to the eye. T he structure t hat is most consistent with all t he above observations for t he high pressure phase is t he space group I r n 3. This is equiva-
P9 TABLE 1 T e m p e r a t u r e - p r e s s u r e values for t h e c o m p r e s s i b i l i t y collapse t r a n s i t i o n in R e O 3
Temperature (K)
Pressure ( k b a r )
Technique
2.00 ± 0.01 76 ± 1 130 ± 6 206 ± 12 223 -+ 12 273 ± 3 296 ± 3
2.45 3.02 3.61 4.50 4.64 5.12 5.22
dHvA NMR NMR NMR NMR NMR NMR
+- 0.10 +- 0.03 -+ 0.03 ± 0.05 +- 0.05 ± 0.05 ± 0.07
lent to a displacement of the oxygen atoms parallel to the (001) plane and perpendicular to the (110) plane, resulting in a hinging of the formerly linear and mutually orthogonal O - - R e - O chains which make up the perovskite structure. This "hinging" at the oxygen atom is an attractive explanation o f the large increase in compressibility. This structure is equivalent to that proposed b y Clarke [5] for the final a+a÷a+ transition which involves rotation of the oxygen octahedra a b o u t the coordinate axes in the NaWOa system. The structure requires a doubling of the lattice parameter and involves a change from simple cubic s y m m e t r y to body-centered cubic symmetry. The point s y m m e t r y at
the rhenium site is reduced from m 3 m to 3. The structure is illustrated in Fig. 5. The latter aspects of the proposed structure change caused some difficulty in reconciliation with the fact that the same Fermi surface was observed in b o t h phases. This difficulty has been removed [6] with the observation of magnetic breakdown effects at very low fields so that the magnetic fields necessary to observe most of the frequencies are far greater than that which is necessary to break d o w n the new energy gaps introduced b y the structure change. Sheets of the Fermi surface of the high pressure phase have now been observed [6] which are completely consistent with the proposed I m 3 structure. Attempts to observe the high pressure phase directly by high pressure X-ray spectroscopy and modest pressure (about 9 kbar) t i m e , f - f l i g h t powder neutron spectroscopy have so far been unsuccessful. Since the oxygen atom displacements are the key to this proposed structure, it is not t o o surprising that the intensities associated with the larger cell have not been observed in diamond cell X-ray diffraction experiments. If we assume that all the distortion of the lattice constant arises from the hinging at the oxygen atom, the maximum deviation from linearity of the O - - R e - O chains is a b o u t 5 ° at 9 kbar and r o o m temperature. Within the estimated standard deviations of our initial neutron powder data refinement and because of the high correlation factor between the oxygen a t o m positional parameters and the oxygen atom thermal parameters (Debye-WaUer factor} we are unable at this time to confirm definitely the oxygen a t o m displacements.
ACKNOWLEDGMENTS
Fig. 5. A s c h e m a t i c r e p r e s e n t a t i o n o f t h e p r o p o s e d high pressure p h a s e o f R e O 3 : o, o x y g e n a t o m s ; o, r h e n i u m a t o m s . Only a t o m s a b o u t t h e p o s i t i o n (0, 0 , 1 ) are s h o w n f o r clarity. R e O 3 o c t a h e d r a are 1 1 1
rotate~..ab°ut the.rhenium positions (.-4+-r'-4+-r'-+7); the orlgmal ambmnt pressure perovsklte cell canabe seen by taking the eight rhenium atoms about the origin.
We acknowledge the expert technical assistance of D. L. Overmyer and R. L. White as well as the cooperation of D. T. Cromer, P. Vergamini and Rex Fluharty. This work was supported b y the U.S. Department of Energy under Contract DEAC04-76-DP00789. Sandia National Laboratories are a U.S. Department of Energy facility.
PIO REFERENCES 1 J. E. Schirber and B. Morosin, Phys. Rev. Lett., 42 (1979) 1485, and references therein. 2 R. K. Quinn and P. G. Neiswander, Mater. Res. Bull., 5 (1970) 329.
3 J. E. Sehirber, L. J. Azevedo and A. Narath, Phys. Rev. B, 20 (1979) 4746. 4 J. E. Schirber, Cryogenics, 10 (1970) 418. 5 R. Clarke, Phys. Rev. Lett., 39 (1977) 1550. 6 J. E. Schirber and D. L. Overmyer, Solid State Commun., 35 (1980) 389.
P7
Phase Diagram of ReO3 in the Vicinity of the "Compressibility Collapse" Transition J. E. SCHIRBER, L. J. A Z E V E D O ,
A. N A R A T H
and B. M O R O S I N
Sandia National Laboratories, Albuquerque, N M 87185 (U.S.A.) (Received February 9, 1981)
SUMMARY
The temperature-pressure phase diagram delineating the "compressibility collapse" transition in the metallic perovskite-structured compound Re03 was determined between 1 and 300 K by a combination o f de Haasvan Alphen and nuclear magnetic resonance measurements as a function o f pressure. The high pressure phase is thought to have a structure with the space group Ira3; this has not yet been verified directly but it is consistent with an increasing amount o f indirect evidence.
1. INTRODUCTION
We have recently [1] identified a novel second-order phase transition in the metallic perovskite-structured compound ReO3. The most unusual property of this transition is that the high pressure phase has a much larger (by a factor of about 7) compressibility than the normal volume phase, giving rise to its designation as the "compressibility collapse" transition. In this paper we present our determination of the temperature- pressure phase boundary which separates the normal volume and the high pressure modifications.
2. EXPERIMENTAL PROCEDURE
The samples were single crystals of roughly millimeter dimensions grown [2] in iodine vapour. The chemical purity of the starting material was determined to be greater than 99.99q% by spectroscopic analysis. These single crystals were of high perfection, as indicated by the electronic mean free paths. Extremely large q u a n t u m oscillations were observed with measured Dingle temperatures 0025-541618110000-00001502.50
(determined from the amplitudes of the de Haas-van Alphen (dHvA) oscillations) which were typically in the temperature range of a few tenths of a kelvin. For the nuclear magnetic resonance (NMR) experiments that we shah discuss, these crystals were powdered so that they passed through a 325 mesh screen. The phase transition was detected (1) by the change in slope of the dHvA crosssectional area with pressure at low temperatures [1], (2) by observation of the change in amplitude of the NMR signal of the lSTRe nucleus due to the onset of first-order quadrupolar effects [3] and (3) by measurements of the lattice constant as a function of pressure at room temperature [1]. The first two techniques were by far the most accurate for determining the phase diagram.
3. RESULTS AND DISCUSSION
A derivative method for measurement of the pressure dependence of the Fermi surface has been developed in which the position in field of a single dHvA oscillation is monitored at pressures of several kilobars [1]. The slope of this position in field or phase is a direct measure of the pressure derivative of the cross section. The pressure is conveniently varied and generated by careful isobaric freezing [4] of helium. In Fig. 1 such a plot for a prominent set of oscillations arising from the a sheet [1] of the Fermi surface is shown. A very sharp break at 2.45 kbar is obsewed, which corresponds to a discontinuous j u m p in the compressibility of ReO3. The data shown comprise four separate excursions through the transition. No sign of hysteresis was observed and the volume change associated with the transition is esti© Elsevier Sequoia/Printed in The Netherlands
P8 I
I
I
61
I
./
/ 32 x I0"4 k b o r ' ~
'/
4w
/ /
00-""%'
5--
II
'
21
Pressure
e
I
,
3
i
,
I
4
(kbar)
Fig. 1. The shift in phase vs. pressure for the ~ frequency of the Fermi suface of ReO 3 for B//[110] at 100 kG. I,(30 - .
We have exploited t he quadrupolar effects on t he lSTRe NMR t o show t hat t h e symm e t r y at t he rheni um site is less t han cubic above t he transition [3]. T he di m i nut i on o f t he amplitude o f t he resonance when t h e 2I (where ! denot es t he t o t a l nuclear spin) first-order satellites move away f r o m t he central ~1 ~_. _ 1-~ line serves as a sensitive indicator o f the onset o f t he transition. The predicted amplitude ratio is 35:9, assuming t h a t all five transitions are observed for the lSVRe nucleus with I --~.5 Figure 3 shows a plot o f such data at 76 K. In Fig. 4 we show t he phase diagram in t h e t e m p e r a t u r e - p r e s s u r e plane for t he compressibility collapse transition det erm i ned using our NMR and dHvA data. We summarize these data in Table 1 t o g e t h e r with t h e uncertainties involved in each det erm i nat i on o f t h e transition.
.9! l-
c
14
>_ 12
~.98
lID
3.9~ l .96
a: >.
8 6
~
4
\i ½ !
_z 2I
½
0:
.95
40 Pressure
3 PRESSURE (kbar)
z
I
210
60 (kbor)
SIC)
I00
Fig. 2. Reduced lattice constant v s . pressure for ReO 3 at room temperature: -- -- --, an extension of the data for pressures below 4 kbar.
mated t o be less t ha n 2 parts in 10 5 (based o n th e sensitivity o f t he phase shift t echni que in this experiment). We cite these factors as evidence t h a t t h e transition is second order in nature. We have verified this j u m p in compressibility b y direct measurements [1] o f t he lattice constant as a f u n c t i o n o f pressure. Our data are shown in Fig. 2. The low pressure slope d eter min ed hydrostatically f r om b o t h p o w d e r studies and single-crystal Weissenberg X-ray studies is shown as a b r o k e n line. Although this clearly shows a large increase in compressibility in t he high pressure state, t h e accuracy o f t he pressure calibration (via a silver internal standard) in t h e d i a m o n d anvil cell is t o o low to d e t e r m i n e t h e phase boundary.
4
Fig. 3. Amplitude (arbitrary units) of the lS7Re nuclear magnetic resonance vs. pressure for ReO 3 at 75 K and a frequency of 10 MHz: . . . . , the theoretically predicted diminution of the amplitude. The vertical arrow is our definition of the transition. i
300
J
I
,.~/
'
I
(
200
~
~-
~/~
½ I00
J
/ 0
2
i/
I
3
,
I
4
PRESSURE:
,
I
5
I
i
6
(kbor)
Fig. 4. Temperature-pressure dependence of the compressibility collapse transition in ReO s. The
full curve is shown only as a guide to the eye. T he structure t hat is most consistent with all t he above observations for t he high pressure phase is t he space group I r n 3. This is equiva-
P9 TABLE 1 T e m p e r a t u r e - p r e s s u r e values for t h e c o m p r e s s i b i l i t y collapse t r a n s i t i o n in R e O 3
Temperature (K)
Pressure ( k b a r )
Technique
2.00 ± 0.01 76 ± 1 130 ± 6 206 ± 12 223 -+ 12 273 ± 3 296 ± 3
2.45 3.02 3.61 4.50 4.64 5.12 5.22
dHvA NMR NMR NMR NMR NMR NMR
+- 0.10 +- 0.03 -+ 0.03 ± 0.05 +- 0.05 ± 0.05 ± 0.07
lent to a displacement of the oxygen atoms parallel to the (001) plane and perpendicular to the (110) plane, resulting in a hinging of the formerly linear and mutually orthogonal O - - R e - O chains which make up the perovskite structure. This "hinging" at the oxygen atom is an attractive explanation o f the large increase in compressibility. This structure is equivalent to that proposed b y Clarke [5] for the final a+a÷a+ transition which involves rotation of the oxygen octahedra a b o u t the coordinate axes in the NaWOa system. The structure requires a doubling of the lattice parameter and involves a change from simple cubic s y m m e t r y to body-centered cubic symmetry. The point s y m m e t r y at
the rhenium site is reduced from m 3 m to 3. The structure is illustrated in Fig. 5. The latter aspects of the proposed structure change caused some difficulty in reconciliation with the fact that the same Fermi surface was observed in b o t h phases. This difficulty has been removed [6] with the observation of magnetic breakdown effects at very low fields so that the magnetic fields necessary to observe most of the frequencies are far greater than that which is necessary to break d o w n the new energy gaps introduced b y the structure change. Sheets of the Fermi surface of the high pressure phase have now been observed [6] which are completely consistent with the proposed I m 3 structure. Attempts to observe the high pressure phase directly by high pressure X-ray spectroscopy and modest pressure (about 9 kbar) t i m e , f - f l i g h t powder neutron spectroscopy have so far been unsuccessful. Since the oxygen atom displacements are the key to this proposed structure, it is not t o o surprising that the intensities associated with the larger cell have not been observed in diamond cell X-ray diffraction experiments. If we assume that all the distortion of the lattice constant arises from the hinging at the oxygen atom, the maximum deviation from linearity of the O - - R e - O chains is a b o u t 5 ° at 9 kbar and r o o m temperature. Within the estimated standard deviations of our initial neutron powder data refinement and because of the high correlation factor between the oxygen a t o m positional parameters and the oxygen atom thermal parameters (Debye-WaUer factor} we are unable at this time to confirm definitely the oxygen a t o m displacements.
ACKNOWLEDGMENTS
Fig. 5. A s c h e m a t i c r e p r e s e n t a t i o n o f t h e p r o p o s e d high pressure p h a s e o f R e O 3 : o, o x y g e n a t o m s ; o, r h e n i u m a t o m s . Only a t o m s a b o u t t h e p o s i t i o n (0, 0 , 1 ) are s h o w n f o r clarity. R e O 3 o c t a h e d r a are 1 1 1
rotate~..ab°ut the.rhenium positions (.-4+-r'-4+-r'-+7); the orlgmal ambmnt pressure perovsklte cell canabe seen by taking the eight rhenium atoms about the origin.
We acknowledge the expert technical assistance of D. L. Overmyer and R. L. White as well as the cooperation of D. T. Cromer, P. Vergamini and Rex Fluharty. This work was supported b y the U.S. Department of Energy under Contract DEAC04-76-DP00789. Sandia National Laboratories are a U.S. Department of Energy facility.
PIO REFERENCES 1 J. E. Schirber and B. Morosin, Phys. Rev. Lett., 42 (1979) 1485, and references therein. 2 R. K. Quinn and P. G. Neiswander, Mater. Res. Bull., 5 (1970) 329.
3 J. E. Sehirber, L. J. Azevedo and A. Narath, Phys. Rev. B, 20 (1979) 4746. 4 J. E. Schirber, Cryogenics, 10 (1970) 418. 5 R. Clarke, Phys. Rev. Lett., 39 (1977) 1550. 6 J. E. Schirber and D. L. Overmyer, Solid State Commun., 35 (1980) 389.