- Email: [email protected]
Structural phase transition in CsNO3: dielectric studies
SOLID STATE IONICS
Solid State lonics 62 ( 1993 ) 293-295 North-Holland
Structural phase transition in
CsNO3: dielectric studies
A. S a d a n a n d a C h a r y , S. N a r e n d e r R e d d y a n d T. C h i r a n j i v i Department of Physics, University College of Science, Osmania University, Hyderabad-500 007, India Received 15 February 1993; accepted for publication 11 May 1993
Dielectric properties - dielectric constant (K), dielectric loss (tan 6) and ac conductivity (a) in the solution grown single crystals of CsNO3 are presented from room temperature to about 230°C covering the frequency range from I00 Hz to 100 KHz. Anomalous behaviour of K, tan 6 and ac a at about 154°C is attributed to the structural phase transition from trigonal to CsC1 cubic structure.
1. Introduction
surements. The data was recorded as reported earlier
[8]. Study o f dielectric properties gives a good insight into the distribution o f electric field in the system. Investigation of K, tan 6 and a as function of frequency and temperature explains the various polarization mechanisms involved. Amongst the alkali nitrates CsNO3 and RbNO3 are structurally isomorphous at room temperature [ 13 ]. CsNO 3 undergoes a phase transition from trigonal to CsC1 cubic structure at about 154°C [4]. It is also known to undergo a transition [ 5 ] at low temperature ( - 35 oC) and two more transitions [ 6 ] at high pressures (4.5 G P a and 12.5 G P a ) which are at room temperature. There have been studies on the variation of K and a with temperature [4], K and tan 6 with frequency [ 7 ] etc., but not on the variation o f all the three parameters K, tan 6 and a with both temperature and frequency which enables a correlation amongst them. An attempt is made to correlate them in this paper.
2. Experimental
3. Results and discussion
3.1. Variation of K and tan 6 with frequency Fig. 1 shows the variation o f dielectric constant with frequency at room temperature. From a value 35
3C
2.c
I
I0
o
,
Starting chemical was from Loba Chemie (India). The salt was dissolved in double distilled water, filtered and allowed to evaporate slowly. The single crystals so obtained were used for dielectric meaElsevier Science Publishers B.V.
10 2
.
.
.
.
.
,,[
,
lO 3
,
,
i
....
I
I0 ~
,
,
-.--.-.o
,
, , , , , J
I05
) Freq ( l-l:z)
Fig. 1. Variation of dielectric constant with frequency at room temperature for CsN03 single crystals.
A. Sadananda Chary et al. /Structuralphase transition in CsN03
294
of about 34 at 100 Hz, K falls to about 10 at 3 KHz and reaches a nearly constant value of about 9 further. This suggests that contribution from all the four - electronic, ionic, relaxational and space charge polarizations is present. The variation of dielectric loss with frequency is shown in fig. 2. Starting from a value of about 2 . 6 × 10 ° at 100 Hz tan 5 falls to 1.7× 10 -1 at 100 KHz with a hump at 30 KHz. This deviation in variation of tan 6 may be due to the contribution from the relaxation of I- V dipoles (unavoidable and soluble impurities in the starting material), in addition to the contribution from the conduction process [9 ]. 3.2. Variation with temperature
Fig. 3 shows the variation of dielectric constant with temperature at different frequencies. The variation seems to be very slight between room temperature and 140°C which rules out the possibility of any major structural change in the system. This slight change in K could be due to the increased mobility of the defects present in the crystal. For 1 KHz, K starts increasing at about 140 ° C which becomes sharp at about 154°C. This corresponds to the known III structural phase transition. For the other two frequencies (10 KHz and 100 KHz) the transition seems to start at higher temperatures. It can be seen that at any given temperature, K decreases with frequency which is in keeping with a fall of K with frequency at room temperature (fig. 1 ). Fig. 4 gives the plot of dielectric loss with temperature at different frequencies. From room temperature tan 5 decreases till about 50°C for each frequency and then slowly increases leading to a peak in the vicinity of the tran-
640 • -o --
800
IO~H~ 10~H~
x -- IOs H~
560
20
I
480
44O 400
36O
i 320 280
/ /
/
24o
200 160 120 80 40
~ / / ~ / J ~ J ~
30
60
90
120
180
150
210
240
Fig. 3. Variation of dielectric constant with temperature at different frequencies in CsNOa single crystals.
o ~ IO~H~ x ~ l0 ~ H~
/ / /
;d uo
id
30
50
70
90
110
130
150
170
190
210 230 250
---~ T'C o~ c
Fig. 4. Variation of dielectric loss with temperature at different frequencies of CsNO3 single crystals.
I
10~
, ,~03
. . . . . . . . .
Freq( H~)
i~0~
iO~
Fig. 2. Dielectric loss versus frequency at room temperature of C s N O 3 single crystals.
sition temperature. The peaks can be seen to shift to higher temperatures as frequency increases - similar to the sudden changes in K at the phase transition temperature described above. These peaks mainly correspond to the relaxational motion of nitrate ion
A. Sadananda Chary et al. /Structuralphase transition in CsN03
295
dc conductivity data in C s N O 3 [ 13 ] where the conductivity is lower than that recorded for the lowest frequency.
[10] with a possibility o f some contribution from the relaxation o f I - V dipoles present in it. N o r m a l l y relaxation peaks shift to higher t e m p e r a t u r e s if frequency is increased [ 11 ] as m o r e energy is required for the relaxation at higher frequency. The peaks observed at the phase transition do not seem to correspond to the h u m p observed at 30 K H z at r o o m t e m p e r a t u r e (fig. 2). This is because o f two reasons. If we go by the concept o f shifting o f peaks to higher t e m p e r a t u r e s at higher frequencies, the peak observed at 30 K H z at r o o m t e m p e r a t u r e ( - ~ 3 0 ° C ) would appear at much higher frequencies at the phase transition t e m p e r a t u r e ( ~ 1 5 4 ° C ) . We also have similar peaks for 1 K H z a n d 10 K H z all o f which are less than 30 KHz. Secondly, m a g n i t u d e o f tan ~ is much higher for the peaks at transition t e m p e r a t u r e as c o m p a r e d to that at r o o m t e m p e r a t u r e implying that c o n t r i b u t i o n to loss from the c o n d u c t i o n process is much m o r e than from dipole relaxations [ 9 ]. Lastly the v a r i a t i o n o f ac c o n d u c t i v i t y with temperature at different frequencies is shown in fig. 5. This dielectric c o n d u c t i v i t y is calculated from K a n d tan ~. It can be noticed that in the trigonal phase conductivity is higher for higher frequencies at any given t e m p e r a t u r e [ 12 ]. This trend seems to extend to the
4. Conclusions The I I - I transition in C s N O 3 at 154°C is from low s y m m e t r y trigonal to high s y m m e t r y CsCI cubic structure. This would facilitate free rotation o f the nitrate ion as well as enhanced mobility o f the defects in the increased space in the high t e m p e r a t u r e phase. Orientational d i s o r d e r and enhanced rotation o f the nitrate ion are supposed to be mainly responsible for the a n o m a l o u s change o f K, tan ~ and a at the transition.
Acknowledgement The authors thank Prof. K.V. Rao, Indian Institute o f Technology, Kharagpur, for the experimental facility and useful discussions.
References
x ~ 10s H~
b id
T
i
1.7
,
,
1.9
i
i
2.1
,
i
2.3
L
I09 1~'
:
2.5
i
,
2-7
i
i
2'.9
,
311
T
Fig. 5. Plot of ac conductivity versus reciprocal temperature at different frequencies in CsNO3 single crystals.
3-3
[ 1] M.H. Brooker, J. Chem. Phys. 68 (1978) 67. [2 ] B.W. Lucas, Acta Cryst. C 39 (1983) 159 I. [3] C. Dean, T.W. Hambley and M.R. Show, Acta Cryst. C 40 (1984) 1512. [4] E. Mariani, J. Dikant, A. Jonova and G.F. Dobrzhanskii, Phys. Status Solidi (a) 31 (1975) 749. [ 5 ] J.H. Fermor and A. Kjekshus, Acta Chem. Scand. 26 (1972) 2645. [6] M.S. Kalliomaki and V.P.J. Meisalo, Acta Cryst. B 35 (1979) 2829. [ 7 ] R. Kawashima and K. Hirai, Philos. Mag. B 58 ( 1988 ) 663. [ 8 ] A. Sadananda Chary, S. Narender Reddy and T. Chiranjivi, J. Mat. Sci. 24 (1989) 2199. [9] E. Mariani, J. Eckstein and E. Rubinova, Czech. J. Phys. B 17 (1967) 552. [ 10] S. Fujimoto, N. Yasuda, H. Shimizu, S. Tsuboi, K. Kawabe, Y. Takagi and M. Midorikawa, J. Phys. Soc. Japan 42 (1977) 911. [ 11 ] B. Tareev, Physics of Dielectric Materials (Mir, Moscow, 1979) p. 159. [ 12] C.J. Leedecke and R.E. Loehman, J. Am. Ceram. Soc. 63 (1980) 190. [ 13 ] A. Sadananda Chary, S. Narender Reddy and T. Chiranjivi, Phase Transit. 9 (1987) 73.
Solid State lonics 62 ( 1993 ) 293-295 North-Holland
Structural phase transition in
CsNO3: dielectric studies
A. S a d a n a n d a C h a r y , S. N a r e n d e r R e d d y a n d T. C h i r a n j i v i Department of Physics, University College of Science, Osmania University, Hyderabad-500 007, India Received 15 February 1993; accepted for publication 11 May 1993
Dielectric properties - dielectric constant (K), dielectric loss (tan 6) and ac conductivity (a) in the solution grown single crystals of CsNO3 are presented from room temperature to about 230°C covering the frequency range from I00 Hz to 100 KHz. Anomalous behaviour of K, tan 6 and ac a at about 154°C is attributed to the structural phase transition from trigonal to CsC1 cubic structure.
1. Introduction
surements. The data was recorded as reported earlier
[8]. Study o f dielectric properties gives a good insight into the distribution o f electric field in the system. Investigation of K, tan 6 and a as function of frequency and temperature explains the various polarization mechanisms involved. Amongst the alkali nitrates CsNO3 and RbNO3 are structurally isomorphous at room temperature [ 13 ]. CsNO 3 undergoes a phase transition from trigonal to CsC1 cubic structure at about 154°C [4]. It is also known to undergo a transition [ 5 ] at low temperature ( - 35 oC) and two more transitions [ 6 ] at high pressures (4.5 G P a and 12.5 G P a ) which are at room temperature. There have been studies on the variation of K and a with temperature [4], K and tan 6 with frequency [ 7 ] etc., but not on the variation o f all the three parameters K, tan 6 and a with both temperature and frequency which enables a correlation amongst them. An attempt is made to correlate them in this paper.
2. Experimental
3. Results and discussion
3.1. Variation of K and tan 6 with frequency Fig. 1 shows the variation o f dielectric constant with frequency at room temperature. From a value 35
3C
2.c
I
I0
o
,
Starting chemical was from Loba Chemie (India). The salt was dissolved in double distilled water, filtered and allowed to evaporate slowly. The single crystals so obtained were used for dielectric meaElsevier Science Publishers B.V.
10 2
.
.
.
.
.
,,[
,
lO 3
,
,
i
....
I
I0 ~
,
,
-.--.-.o
,
, , , , , J
I05
) Freq ( l-l:z)
Fig. 1. Variation of dielectric constant with frequency at room temperature for CsN03 single crystals.
A. Sadananda Chary et al. /Structuralphase transition in CsN03
294
of about 34 at 100 Hz, K falls to about 10 at 3 KHz and reaches a nearly constant value of about 9 further. This suggests that contribution from all the four - electronic, ionic, relaxational and space charge polarizations is present. The variation of dielectric loss with frequency is shown in fig. 2. Starting from a value of about 2 . 6 × 10 ° at 100 Hz tan 5 falls to 1.7× 10 -1 at 100 KHz with a hump at 30 KHz. This deviation in variation of tan 6 may be due to the contribution from the relaxation of I- V dipoles (unavoidable and soluble impurities in the starting material), in addition to the contribution from the conduction process [9 ]. 3.2. Variation with temperature
Fig. 3 shows the variation of dielectric constant with temperature at different frequencies. The variation seems to be very slight between room temperature and 140°C which rules out the possibility of any major structural change in the system. This slight change in K could be due to the increased mobility of the defects present in the crystal. For 1 KHz, K starts increasing at about 140 ° C which becomes sharp at about 154°C. This corresponds to the known III structural phase transition. For the other two frequencies (10 KHz and 100 KHz) the transition seems to start at higher temperatures. It can be seen that at any given temperature, K decreases with frequency which is in keeping with a fall of K with frequency at room temperature (fig. 1 ). Fig. 4 gives the plot of dielectric loss with temperature at different frequencies. From room temperature tan 5 decreases till about 50°C for each frequency and then slowly increases leading to a peak in the vicinity of the tran-
640 • -o --
800
IO~H~ 10~H~
x -- IOs H~
560
20
I
480
44O 400
36O
i 320 280
/ /
/
24o
200 160 120 80 40
~ / / ~ / J ~ J ~
30
60
90
120
180
150
210
240
Fig. 3. Variation of dielectric constant with temperature at different frequencies in CsNOa single crystals.
o ~ IO~H~ x ~ l0 ~ H~
/ / /
;d uo
id
30
50
70
90
110
130
150
170
190
210 230 250
---~ T'C o~ c
Fig. 4. Variation of dielectric loss with temperature at different frequencies of CsNO3 single crystals.
I
10~
, ,~03
. . . . . . . . .
Freq( H~)
i~0~
iO~
Fig. 2. Dielectric loss versus frequency at room temperature of C s N O 3 single crystals.
sition temperature. The peaks can be seen to shift to higher temperatures as frequency increases - similar to the sudden changes in K at the phase transition temperature described above. These peaks mainly correspond to the relaxational motion of nitrate ion
A. Sadananda Chary et al. /Structuralphase transition in CsN03
295
dc conductivity data in C s N O 3 [ 13 ] where the conductivity is lower than that recorded for the lowest frequency.
[10] with a possibility o f some contribution from the relaxation o f I - V dipoles present in it. N o r m a l l y relaxation peaks shift to higher t e m p e r a t u r e s if frequency is increased [ 11 ] as m o r e energy is required for the relaxation at higher frequency. The peaks observed at the phase transition do not seem to correspond to the h u m p observed at 30 K H z at r o o m t e m p e r a t u r e (fig. 2). This is because o f two reasons. If we go by the concept o f shifting o f peaks to higher t e m p e r a t u r e s at higher frequencies, the peak observed at 30 K H z at r o o m t e m p e r a t u r e ( - ~ 3 0 ° C ) would appear at much higher frequencies at the phase transition t e m p e r a t u r e ( ~ 1 5 4 ° C ) . We also have similar peaks for 1 K H z a n d 10 K H z all o f which are less than 30 KHz. Secondly, m a g n i t u d e o f tan ~ is much higher for the peaks at transition t e m p e r a t u r e as c o m p a r e d to that at r o o m t e m p e r a t u r e implying that c o n t r i b u t i o n to loss from the c o n d u c t i o n process is much m o r e than from dipole relaxations [ 9 ]. Lastly the v a r i a t i o n o f ac c o n d u c t i v i t y with temperature at different frequencies is shown in fig. 5. This dielectric c o n d u c t i v i t y is calculated from K a n d tan ~. It can be noticed that in the trigonal phase conductivity is higher for higher frequencies at any given t e m p e r a t u r e [ 12 ]. This trend seems to extend to the
4. Conclusions The I I - I transition in C s N O 3 at 154°C is from low s y m m e t r y trigonal to high s y m m e t r y CsCI cubic structure. This would facilitate free rotation o f the nitrate ion as well as enhanced mobility o f the defects in the increased space in the high t e m p e r a t u r e phase. Orientational d i s o r d e r and enhanced rotation o f the nitrate ion are supposed to be mainly responsible for the a n o m a l o u s change o f K, tan ~ and a at the transition.
Acknowledgement The authors thank Prof. K.V. Rao, Indian Institute o f Technology, Kharagpur, for the experimental facility and useful discussions.
References
x ~ 10s H~
b id
T
i
1.7
,
,
1.9
i
i
2.1
,
i
2.3
L
I09 1~'
:
2.5
i
,
2-7
i
i
2'.9
,
311
T
Fig. 5. Plot of ac conductivity versus reciprocal temperature at different frequencies in CsNO3 single crystals.
3-3
[ 1] M.H. Brooker, J. Chem. Phys. 68 (1978) 67. [2 ] B.W. Lucas, Acta Cryst. C 39 (1983) 159 I. [3] C. Dean, T.W. Hambley and M.R. Show, Acta Cryst. C 40 (1984) 1512. [4] E. Mariani, J. Dikant, A. Jonova and G.F. Dobrzhanskii, Phys. Status Solidi (a) 31 (1975) 749. [ 5 ] J.H. Fermor and A. Kjekshus, Acta Chem. Scand. 26 (1972) 2645. [6] M.S. Kalliomaki and V.P.J. Meisalo, Acta Cryst. B 35 (1979) 2829. [ 7 ] R. Kawashima and K. Hirai, Philos. Mag. B 58 ( 1988 ) 663. [ 8 ] A. Sadananda Chary, S. Narender Reddy and T. Chiranjivi, J. Mat. Sci. 24 (1989) 2199. [9] E. Mariani, J. Eckstein and E. Rubinova, Czech. J. Phys. B 17 (1967) 552. [ 10] S. Fujimoto, N. Yasuda, H. Shimizu, S. Tsuboi, K. Kawabe, Y. Takagi and M. Midorikawa, J. Phys. Soc. Japan 42 (1977) 911. [ 11 ] B. Tareev, Physics of Dielectric Materials (Mir, Moscow, 1979) p. 159. [ 12] C.J. Leedecke and R.E. Loehman, J. Am. Ceram. Soc. 63 (1980) 190. [ 13 ] A. Sadananda Chary, S. Narender Reddy and T. Chiranjivi, Phase Transit. 9 (1987) 73.