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35Cl nuclear quadrupolar resonance study of 4,4′-dichlorobiphenyl sulphone
Volume 114A, n u m b e r 2
PHYSICS LETTERS
3 February 1986
3sCl NUCLEAR QUADRUPOLAR RESONANCE STUDY OF 4,4'-DICHLOROBIPHENYL SULPHONE J.M. CORBERO, A.E. WOLFENSON 1, D.J. PUSIOL 2 and A.H. BRUNETTI 2 Facultad de Materniztica, Astronom'ta y Ytsica (IMAF), Unioersidad Nacional de Cbrdoba, Laprida 854, 5000 Cbrdoba, Argentina Received 18 June 1985; revised manuscript received 6 September 1985; accepted for publication 10 October 1985
Pulsed N Q R spectroscopy was used to search for a structural phase transition from a normal to an incommensurate phase and others in 4,4'-dichlorobiphenyl sulphone. The experimental results show the existence of a structural phase transition to an incommensurate phase at 150 K and another transition to a possible commensurate phase at 110 K.
There has been a growing interest in biphenyl (C12H10) molecular crystals over the last years, since it was found that they exhibit several solid-solid phase transitions, which probably include two incommensurate phases [ 1,2 ]. However, no commensurate phases have been found in this crystal at low temperature. These features, as well as the successive appearance of two different incommensurate phases, still have no plausible explanation. Blinc [3] has shown that nuclear quadrupolar resonance (NQR) is a very powerful technique to study commensurate and incommensurate systems. Indeed, from the temperature dependence of both the NQR frequency, vq(T), and line intensity, I(T), it can be determined whether the system goes from a high temperature normal phase to an incommensurate one [4]. Although the 4,4' dichlorobiphenyl sulphone is a similar molecular compound to biphenyl, we observed some differences in its phase diagram. A 35C1NQR study of 4,4' dichlorobiphenyl sulphone shows prelim. inary results which are somewhat different to those observed for biphenyl crystals. The results show that in the temperature range of 340 to 87 K the sample 1 Holder of a fellowship of the Consejo Nacional de Investigaciones Cientificas y Tdcnicas (Argentina). 2 Fellow of the Consejo Nacional de Investigaciones Cientificas y Tdcnicas (Argentina).
0.375-9601]86/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
undergoes first a structural phase transition (SPT) from a high temperature normal phase to an incommensurate phase; and further down from the incommensurate to a possible commensurate phase. Measurements of vq(T) were performed by means of a conventional pulsed NQR spectrometer. For tem. peratures higher than Ti = 150 K only one sharp resonance line was observed indicating only one distinct site for the 35 C1 nuclei. The temperature behaviour of vq(T), in this temperature range, is normal and the-experimental data is well fitted by the Bayer-Kushida theory (BK) [5].In the range 115 K < T < 150 K two resonance lines were observed, indicating the presence of two sites. The high frequency line is seven times wider than the low frequency one; this difference was observed because the NQR technique is very sensitive to detect electric field gradient (VE) changes, then any crystalline disorder which affects the VE produces a widening of the NQR line. The low frequency line does not show a marked line width change through the phase transition. Although these are qualitative results they give important information. Below T e = 1 i5 K, the high frequency line abruptly disappears and only one resonance line, as a continuation of the low frequency line, was observed. Fig. 1 shows vq(T) in the temperature range 87 K < T < 160 K. The graph shows a continuous splitting of the two lines below 150 K and the abrupt disappearance of the high frequency line. This type of behav105
Volume 114A, number 2
PHYSICS LETTERS 250
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3 February 1986 I
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iour is similar to that observed in systems which undergoes normal-incommensurate-commensurate structures [4,6]. A possible explanation of this discontinuous change of the NQR spectrum is that the crystalline sample undergoes an incommensurate to a commensurate structure which take place in the lower temperature range. Fig. 2 depicts the intensity data versus T. As the temperature is lowered from 340 K the line intensity increases following the Curie law. For T < 185 K, I(T) decreases dramatically as the temperature is lowered towards 150 K. The intensity lost can be associated with an extra broad resonance line as a precursor to the SPT to an incommensurate phase. As T is lowered towards 115 K both line intensities increase recovering the total intensity, however each line intensity reaches approximately 1/2 o f the value respect to the intensity just above 185 K. The intensity temperature behaviour observed for 4,4' dichlorobiphenyl sulphone is qualitatively similar to that observed for
106
Fig. 2. Line intensity versus temperature: • corresponds to the high frequency line in fig. 1; • corresponds to the low frequency line in the temperature range up to 150 K and the single line above that temperature. Rb2ZnC12 [4], which has a ferroelectric incommensurate-commensurate phase diagram. Concluding, uq(T) and I(T) data allow us to interpret that 4,4 dichlorobiphenyl sulphone undergoes a SPT from a normal to an incommensurate phase at 150 K and a possible incommensurate to commensurate phase transition at 115 K.
References [1] A. Cullick and R.E. Gerkin, Chem. Phys. 23 (1977) 277. [2] M. Wada, A. Sarvada and Y. lshibaske, J. Phys. Soc. Japan 50 (1981) 737. [3] R. Blinc, Phys. Rep. 79 (1981) 331. [4] F. Millia and V. Rutar, Phys. Rev. B23 (1981) 6061. [5] T. Kushida, G.B. Benedeck and N. Bloembergen, Phys. Rev. 104 (1956) 1364. [6] R. Ambrosetti, R. Angelone, A. Colligiani and A. Rigamonti, Phys. Rev. B15 (1977) 4318.
PHYSICS LETTERS
3 February 1986
3sCl NUCLEAR QUADRUPOLAR RESONANCE STUDY OF 4,4'-DICHLOROBIPHENYL SULPHONE J.M. CORBERO, A.E. WOLFENSON 1, D.J. PUSIOL 2 and A.H. BRUNETTI 2 Facultad de Materniztica, Astronom'ta y Ytsica (IMAF), Unioersidad Nacional de Cbrdoba, Laprida 854, 5000 Cbrdoba, Argentina Received 18 June 1985; revised manuscript received 6 September 1985; accepted for publication 10 October 1985
Pulsed N Q R spectroscopy was used to search for a structural phase transition from a normal to an incommensurate phase and others in 4,4'-dichlorobiphenyl sulphone. The experimental results show the existence of a structural phase transition to an incommensurate phase at 150 K and another transition to a possible commensurate phase at 110 K.
There has been a growing interest in biphenyl (C12H10) molecular crystals over the last years, since it was found that they exhibit several solid-solid phase transitions, which probably include two incommensurate phases [ 1,2 ]. However, no commensurate phases have been found in this crystal at low temperature. These features, as well as the successive appearance of two different incommensurate phases, still have no plausible explanation. Blinc [3] has shown that nuclear quadrupolar resonance (NQR) is a very powerful technique to study commensurate and incommensurate systems. Indeed, from the temperature dependence of both the NQR frequency, vq(T), and line intensity, I(T), it can be determined whether the system goes from a high temperature normal phase to an incommensurate one [4]. Although the 4,4' dichlorobiphenyl sulphone is a similar molecular compound to biphenyl, we observed some differences in its phase diagram. A 35C1NQR study of 4,4' dichlorobiphenyl sulphone shows prelim. inary results which are somewhat different to those observed for biphenyl crystals. The results show that in the temperature range of 340 to 87 K the sample 1 Holder of a fellowship of the Consejo Nacional de Investigaciones Cientificas y Tdcnicas (Argentina). 2 Fellow of the Consejo Nacional de Investigaciones Cientificas y Tdcnicas (Argentina).
0.375-9601]86/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
undergoes first a structural phase transition (SPT) from a high temperature normal phase to an incommensurate phase; and further down from the incommensurate to a possible commensurate phase. Measurements of vq(T) were performed by means of a conventional pulsed NQR spectrometer. For tem. peratures higher than Ti = 150 K only one sharp resonance line was observed indicating only one distinct site for the 35 C1 nuclei. The temperature behaviour of vq(T), in this temperature range, is normal and the-experimental data is well fitted by the Bayer-Kushida theory (BK) [5].In the range 115 K < T < 150 K two resonance lines were observed, indicating the presence of two sites. The high frequency line is seven times wider than the low frequency one; this difference was observed because the NQR technique is very sensitive to detect electric field gradient (VE) changes, then any crystalline disorder which affects the VE produces a widening of the NQR line. The low frequency line does not show a marked line width change through the phase transition. Although these are qualitative results they give important information. Below T e = 1 i5 K, the high frequency line abruptly disappears and only one resonance line, as a continuation of the low frequency line, was observed. Fig. 1 shows vq(T) in the temperature range 87 K < T < 160 K. The graph shows a continuous splitting of the two lines below 150 K and the abrupt disappearance of the high frequency line. This type of behav105
Volume 114A, number 2
PHYSICS LETTERS 250
34~,5
3 February 1986 I
I
I
\. o\.
, ,
§
"T.
/
20O
_=
)K 34.80
]
I
1
I
\ o\ \\ '\
~o ~[
2
ii
|~
'
..= 34.75
tTc
tTo
-'.
TEMPERATU~I[ { l )
• O\o lOO
t
l
Tc
rl
100
150
"-~. "~% 25O
3
TEMPERATURE ( K )
iour is similar to that observed in systems which undergoes normal-incommensurate-commensurate structures [4,6]. A possible explanation of this discontinuous change of the NQR spectrum is that the crystalline sample undergoes an incommensurate to a commensurate structure which take place in the lower temperature range. Fig. 2 depicts the intensity data versus T. As the temperature is lowered from 340 K the line intensity increases following the Curie law. For T < 185 K, I(T) decreases dramatically as the temperature is lowered towards 150 K. The intensity lost can be associated with an extra broad resonance line as a precursor to the SPT to an incommensurate phase. As T is lowered towards 115 K both line intensities increase recovering the total intensity, however each line intensity reaches approximately 1/2 o f the value respect to the intensity just above 185 K. The intensity temperature behaviour observed for 4,4' dichlorobiphenyl sulphone is qualitatively similar to that observed for
106
Fig. 2. Line intensity versus temperature: • corresponds to the high frequency line in fig. 1; • corresponds to the low frequency line in the temperature range up to 150 K and the single line above that temperature. Rb2ZnC12 [4], which has a ferroelectric incommensurate-commensurate phase diagram. Concluding, uq(T) and I(T) data allow us to interpret that 4,4 dichlorobiphenyl sulphone undergoes a SPT from a normal to an incommensurate phase at 150 K and a possible incommensurate to commensurate phase transition at 115 K.
References [1] A. Cullick and R.E. Gerkin, Chem. Phys. 23 (1977) 277. [2] M. Wada, A. Sarvada and Y. lshibaske, J. Phys. Soc. Japan 50 (1981) 737. [3] R. Blinc, Phys. Rep. 79 (1981) 331. [4] F. Millia and V. Rutar, Phys. Rev. B23 (1981) 6061. [5] T. Kushida, G.B. Benedeck and N. Bloembergen, Phys. Rev. 104 (1956) 1364. [6] R. Ambrosetti, R. Angelone, A. Colligiani and A. Rigamonti, Phys. Rev. B15 (1977) 4318.