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Lattice dimerization and strain in inorganic spin-Peierls compound NaV2O5
ELSEVIER
Physica B 241 243 11998) 534 536
Lattice dimerization and strain in inorganic spin-Peierls compound NaV205 H. Nakao"'*, K. Ohwada a, N. Takesu&, Y. FujiP, M. Isobe b, Y. Ueda b, H. Sawa ~, H. Kawada d' 1, y. Murakami d, W.I.F. David e, R.M. Ibberson e ~Neutron Scattering Laborato~T, lnstituteJbr Solid State Physics. The Universi O, of Tokyo, 106-1 Shirakata. Tokai. lbaraki 319-11, Japan b lnstitutejbr Solid State Physics, The University O/Tolg,o. 7-22-1 Roppongi. Minato-ku. Tokyo 106. Japan ~Department of Physics, FaculO, of Science. Chiba UnirersiO,, 1-33 Yco'oi-cho. lnage-ku. Chiba 263, Japan d Photon Faetoo', Institute of Materia# Structure Science, l-I Oho, Tsukuba, lbaraki 305, Japan IS1S Facility, Rutherlord Appleton Laboraml T. Chilmn, Didcot. Oxon OXI 10QX. UK
Abstract
X-ray and neutron scattering experiments of the new inorganic spin-Peierls compound show that below T~p = 36 K an anomalous volume expansion is proportional to the superlattice intensity associated with lattice dimerization. Also reported is the pressure effect on this compound which undergoes a phase transition around 13 GPa (room temperature). ~(" 1998 Elsevier Science B.V. All rights reserved.
Keywords: Spin-Peierls~ Phase transition; Critical phenomena: NaV205
Recently, Isobe and Ueda [1] successfully synthesized a high-quality inorganic compound ¢(NaV205 and discovered a spin-Peierls behavior in its magnetic susceptibility below T~p. It is the second inorganic spin-Peierls compounds after CuGeO3 [2]. Its space group is P21mn (a=ll.318,b=3.611,c=4.797Aat room temperature) [3]. In the ab-plane there are magnetic V '~+ (S = ½) and nonmagnetic V 5+ (S = 0) chains running along the b-axis. The fact that the magnetic chains are well separated by the nonmagnetic *Corresponding author. Fax: + 81 3 3402 9449: e-mail: [email protected] p. 1present address: Kawada Research Corporation, 5-9-9 Tsukuba Research Consortium, Tokodai, Tsukuba, lbaraki 300-26, Japan.
V ~+ ones implies that the structure is a better candidate for a l-D spin-Peierls system than CuGeO3. By using X-ray and neutron scattering, Fujii et al. found evidence of lattice dimerization spin-gap formation at with q = 1!_1 1,2, 2, !~ 41 and q = (1,½,0) below Tsp [4]. It is also of interest in this compound that the Na-deficiency creates nonmagnetic V 5+ ions in the magnetic V 4+ linear chains, resulting in a finite length of the magnetic chains. Magnetic susceptibility measurements show a remarkable suppression of the spin-Peierls transition with Na-deficiency, vanishing around x = 0.97 for NaxV205 [5]. The purpose of the present work is to investigate critical behavior of this spin-Peierls system near T~p. We have performed X-ray and neutron
0921-4526/98/$19.00 ~' 1998 Elsevier Science B.V. All rights reserved PII S 0 9 2 1 - 4 5 2 6 ( 9 7 ) 0 0 6 3 6 - 4
14. Nakao et al. / Physica B 241 243 (1998) 534 536
lattice C o a s t a t s
535
$uperlattice Reflection
11.3060 11.3055
1.2
.
.
.
1.0
...'.,.|.,.
08
"%
11.3050
~I
.
.
.
! • " " ":* "
• NaV205 - Nao.99V205 o Nao.~V205 • Na0.~V20s " Nao.~V205
..
m '~
1.3IM5
~ 11.3040
11.6
l 1.3035
0.,
",
\
-q'.
"
•
I 1.3030
|
:.--
... *
um
•
x
I
l 1.3025
0.0
a
t
,"
o
Criacal Scattering
3.6110
.~
*~,.~ 3.6109
o8
'
t---
"
'
-
'
."~x: oo
,~ 3.6108
06
~
3.6107
•
° ° , "'
11.4
;g
.
I
I
I
"~ ~,~
0.0
4.756
oe,° oeo°
~,
4.752
Fig. 1. Temperature NaV2Os.
+# ",
• a I" ~'~'~" ,
I
[
I
I
20
40
60
80
Temperature(K)
dependence
]0
....
]5
"-'-*';'z"ts
•
~o
4 4 ",,,° ! "*'..~ oO oi ° o" "~
"I
I-"
,%,V"
"-::,aT', :
2o 25 3o 35 Temperature(K)
" •
," ,
4o
"+ 1
45
Fig. 2. Temperature dependence of superlanice intensity at (3/2,1/'2,11/4) and critical scattering at q = (1.475,0.489,2.70) in Na~V205 (x = 1.00 - 0.95).
4.754
4.750
x
•. " " "
4.758 *~
0.2
,
t
.o.. .tl v .%..
0O'°o
3.6106
"
100
of lattice constants of
scattering experiments to study lattice properties of NaxV205 (x = 1.00-0.95) at low temperatures (room pressure) and at high pressures (room temperature). Neutron powder diffraction experiments using 12.67g of sample were carried out on HRPD(Ad/d ~ 5 x 10 -4) at ISIS. The temperature dependence of lattice constants is shown in Fig. 1. All lattice constants are found to show an anomaly below T+o = 36 K. Above Tso, both the a- and caxis expand normally while the b-axis (the chain direction) anomalously contracts. Below T+p, the only significant changes are reassociated with the c-axis which contracts on approaching Tsp. Similar effects are observed in CuGeO3 [6]. The resultant anomalous unit cell volume expansion
AV is found to be proportional to the 1 3 ! 11~ superlattice intensity ~2, 2, 41 as shown in Fig. 2, upper part, i.e. AV oc I oc 62, where 6 is an atomic displacement associated with lattice dimerization. High-pressure powder X-ray scattering experiments were performed at the Photon Factory. The c-axis is very compressible, while the a- and b-axis unusually expand under high pressure. Furthermore, we discovered that this crystal undergoes a structural phase transition at about 13 GPa. This structure behavior is currently being investigated in detail. X-ray critical scattering measurements were performed using single crystals. In Fig. 2 we show the concentration x dependence of superlattice intensity in the Na-deficient samples NaxV2Os (x = 1 . 0 0 - 0.95). The spin-Peierls transition temperature Tsp is also very sensitively suppressed by the Na-deficiency. The critical scattering associated with the lattice fluctuation in the vicinity of Tsp is clearly observed near the superlattice peak position (at bottom of Fig. 2).
536
H. Nakao et al. / Physica B 241 243 (1998) 534 536
It is f u n d a m e n t a l l y i m p o r t a n t in ~'-NaVzO5 whether such a critical scattering originates from any soft p h o n o n associated with lattice fluctuation e n h a n c e d near Tsp, in contrast to C u G e O 3 in which n o soft p h o n o n behavior has been reported. At present we are p l a n n i n g a n e u t r o n scattering study of soft p h o n o n in this new c o m p o u n d .
References [1] [2] [3] [4] [5] [6]
M. lsobe et al., J. Phys. Soc. Japan 65 (1996) 1178. M. Hase et al., Phys. Rev. Lett. 70 (1993) 3651. P.A. Carpy et al., Acta Crystallogr. Sect. B 31 (1975) 1481. Y. Fujii et al., J. Phys. Soc. Japan 66 (1997) 326. M. Isobe et al., J. Alloys Compounds, submitted. M. Fujita et al., Physica B 213&214 (1995) 288.
Physica B 241 243 11998) 534 536
Lattice dimerization and strain in inorganic spin-Peierls compound NaV205 H. Nakao"'*, K. Ohwada a, N. Takesu&, Y. FujiP, M. Isobe b, Y. Ueda b, H. Sawa ~, H. Kawada d' 1, y. Murakami d, W.I.F. David e, R.M. Ibberson e ~Neutron Scattering Laborato~T, lnstituteJbr Solid State Physics. The Universi O, of Tokyo, 106-1 Shirakata. Tokai. lbaraki 319-11, Japan b lnstitutejbr Solid State Physics, The University O/Tolg,o. 7-22-1 Roppongi. Minato-ku. Tokyo 106. Japan ~Department of Physics, FaculO, of Science. Chiba UnirersiO,, 1-33 Yco'oi-cho. lnage-ku. Chiba 263, Japan d Photon Faetoo', Institute of Materia# Structure Science, l-I Oho, Tsukuba, lbaraki 305, Japan IS1S Facility, Rutherlord Appleton Laboraml T. Chilmn, Didcot. Oxon OXI 10QX. UK
Abstract
X-ray and neutron scattering experiments of the new inorganic spin-Peierls compound show that below T~p = 36 K an anomalous volume expansion is proportional to the superlattice intensity associated with lattice dimerization. Also reported is the pressure effect on this compound which undergoes a phase transition around 13 GPa (room temperature). ~(" 1998 Elsevier Science B.V. All rights reserved.
Keywords: Spin-Peierls~ Phase transition; Critical phenomena: NaV205
Recently, Isobe and Ueda [1] successfully synthesized a high-quality inorganic compound ¢(NaV205 and discovered a spin-Peierls behavior in its magnetic susceptibility below T~p. It is the second inorganic spin-Peierls compounds after CuGeO3 [2]. Its space group is P21mn (a=ll.318,b=3.611,c=4.797Aat room temperature) [3]. In the ab-plane there are magnetic V '~+ (S = ½) and nonmagnetic V 5+ (S = 0) chains running along the b-axis. The fact that the magnetic chains are well separated by the nonmagnetic *Corresponding author. Fax: + 81 3 3402 9449: e-mail: [email protected] p. 1present address: Kawada Research Corporation, 5-9-9 Tsukuba Research Consortium, Tokodai, Tsukuba, lbaraki 300-26, Japan.
V ~+ ones implies that the structure is a better candidate for a l-D spin-Peierls system than CuGeO3. By using X-ray and neutron scattering, Fujii et al. found evidence of lattice dimerization spin-gap formation at with q = 1!_1 1,2, 2, !~ 41 and q = (1,½,0) below Tsp [4]. It is also of interest in this compound that the Na-deficiency creates nonmagnetic V 5+ ions in the magnetic V 4+ linear chains, resulting in a finite length of the magnetic chains. Magnetic susceptibility measurements show a remarkable suppression of the spin-Peierls transition with Na-deficiency, vanishing around x = 0.97 for NaxV205 [5]. The purpose of the present work is to investigate critical behavior of this spin-Peierls system near T~p. We have performed X-ray and neutron
0921-4526/98/$19.00 ~' 1998 Elsevier Science B.V. All rights reserved PII S 0 9 2 1 - 4 5 2 6 ( 9 7 ) 0 0 6 3 6 - 4
14. Nakao et al. / Physica B 241 243 (1998) 534 536
lattice C o a s t a t s
535
$uperlattice Reflection
11.3060 11.3055
1.2
.
.
.
1.0
...'.,.|.,.
08
"%
11.3050
~I
.
.
.
! • " " ":* "
• NaV205 - Nao.99V205 o Nao.~V205 • Na0.~V20s " Nao.~V205
..
m '~
1.3IM5
~ 11.3040
11.6
l 1.3035
0.,
",
\
-q'.
"
•
I 1.3030
|
:.--
... *
um
•
x
I
l 1.3025
0.0
a
t
,"
o
Criacal Scattering
3.6110
.~
*~,.~ 3.6109
o8
'
t---
"
'
-
'
."~x: oo
,~ 3.6108
06
~
3.6107
•
° ° , "'
11.4
;g
.
I
I
I
"~ ~,~
0.0
4.756
oe,° oeo°
~,
4.752
Fig. 1. Temperature NaV2Os.
+# ",
• a I" ~'~'~" ,
I
[
I
I
20
40
60
80
Temperature(K)
dependence
]0
....
]5
"-'-*';'z"ts
•
~o
4 4 ",,,° ! "*'..~ oO oi ° o" "~
"I
I-"
,%,V"
"-::,aT', :
2o 25 3o 35 Temperature(K)
" •
," ,
4o
"+ 1
45
Fig. 2. Temperature dependence of superlanice intensity at (3/2,1/'2,11/4) and critical scattering at q = (1.475,0.489,2.70) in Na~V205 (x = 1.00 - 0.95).
4.754
4.750
x
•. " " "
4.758 *~
0.2
,
t
.o.. .tl v .%..
0O'°o
3.6106
"
100
of lattice constants of
scattering experiments to study lattice properties of NaxV205 (x = 1.00-0.95) at low temperatures (room pressure) and at high pressures (room temperature). Neutron powder diffraction experiments using 12.67g of sample were carried out on HRPD(Ad/d ~ 5 x 10 -4) at ISIS. The temperature dependence of lattice constants is shown in Fig. 1. All lattice constants are found to show an anomaly below T+o = 36 K. Above Tso, both the a- and caxis expand normally while the b-axis (the chain direction) anomalously contracts. Below T+p, the only significant changes are reassociated with the c-axis which contracts on approaching Tsp. Similar effects are observed in CuGeO3 [6]. The resultant anomalous unit cell volume expansion
AV is found to be proportional to the 1 3 ! 11~ superlattice intensity ~2, 2, 41 as shown in Fig. 2, upper part, i.e. AV oc I oc 62, where 6 is an atomic displacement associated with lattice dimerization. High-pressure powder X-ray scattering experiments were performed at the Photon Factory. The c-axis is very compressible, while the a- and b-axis unusually expand under high pressure. Furthermore, we discovered that this crystal undergoes a structural phase transition at about 13 GPa. This structure behavior is currently being investigated in detail. X-ray critical scattering measurements were performed using single crystals. In Fig. 2 we show the concentration x dependence of superlattice intensity in the Na-deficient samples NaxV2Os (x = 1 . 0 0 - 0.95). The spin-Peierls transition temperature Tsp is also very sensitively suppressed by the Na-deficiency. The critical scattering associated with the lattice fluctuation in the vicinity of Tsp is clearly observed near the superlattice peak position (at bottom of Fig. 2).
536
H. Nakao et al. / Physica B 241 243 (1998) 534 536
It is f u n d a m e n t a l l y i m p o r t a n t in ~'-NaVzO5 whether such a critical scattering originates from any soft p h o n o n associated with lattice fluctuation e n h a n c e d near Tsp, in contrast to C u G e O 3 in which n o soft p h o n o n behavior has been reported. At present we are p l a n n i n g a n e u t r o n scattering study of soft p h o n o n in this new c o m p o u n d .
References [1] [2] [3] [4] [5] [6]
M. lsobe et al., J. Phys. Soc. Japan 65 (1996) 1178. M. Hase et al., Phys. Rev. Lett. 70 (1993) 3651. P.A. Carpy et al., Acta Crystallogr. Sect. B 31 (1975) 1481. Y. Fujii et al., J. Phys. Soc. Japan 66 (1997) 326. M. Isobe et al., J. Alloys Compounds, submitted. M. Fujita et al., Physica B 213&214 (1995) 288.