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Splitting of the 23Na NMR central line in ferroelectric AgNa(NO2)2
Volume 37A, number 2
PHYSICS
SPLITTING IN
OF THE 23 Na FERROELECTRIC
T. HIKITA, Research
Institute
LETTERS
of Applied
8 November 1971
NMR CENTRAL AgNa(N02)2
LINE
M. KASAHARA and I. TATSUZAKI Electricity,
Hokkaido
University,
Sapporo,
Japan
Received 11 September 1971 23 Splitting of the Na central line in AgNa(N02)2 was observed in the ferroelectric gradient-tensor in the ferroelectric phase and the paraelectric phase is discussed.
In a recent publication [l], the temperature dependence of the 23 Na quadrupole coupling constant (e2@/h) and the values of the principal components of the 23 Na electricfield-gradient tensor in the ferroelectric and paraelectric phase have been reported. Later, it was found that at certain angles of the b-rotation there is a remarkable line broadening in the ferroelectric phase. In order to obtain the correct shapes of the central line, the modulation amplitude was reduced as much as possible. It was revealed that the central line splits in the ferroelectric phase. The line shapes of the 23Na resonance in both phases are illustrated in fig. 1. This is not istent with the proposed space group DiE v [2]. It permits existence of two equivalent ? ield gradients with some restriction described below, resulting in the two central lines for the b-rotation. Each b-rotation pattern of the second order shift of the two 23Na central components in the ferroelectric phase has been obtained by calculating the separation of the two components. Since the splitting is not complete, the separation was calculated from the broadening. Line broadening versus separation has been computed by numerically superposing two Gaussian lines using a computer [3]. The two shift patterns are identical in sh&pe and symmetric with their symmetric points shifted from the origin about f 4 degrees, the average being the previously observed one. The a- and c-rotation patterns were also taken both in the ferroelectric and in the paraelectric phase. No splitting was observed for these rotations, and the line widths are almost temperature independent. These patterns are all symmetric about the angle at which the crystalline axis is parallel to the magnetic field. Thus we confirm that the principal axes coincide
phase. 23Na field-
Fig. 1. Line shapes of the (c, Ho) = 64’
(b I Ho).
23
Na resonance at ,X in the magnetic field 7100 G.
with the crystalline axes in the paraelectric phase. In the ferroelectric phase there exist two equivalent field gradients whose principal coordinate systems are rotated in the opposite directions to each other about 4 degrees from the crystalline axes around the b-axis. Though in such coordinate systems one rotation about a crystalline axis is sufficient to calculate the values of the principal components, calculation has been made for the three rotation patterns in both phases. Agreement is not gratifying. This seems to be due to the existence of the distribution in the field gradient. If the field gradient at Na differs from site to site, it would effect to the line and give considerable error to the calculation of the field gradient from the rotation pattern. A calculation method taking account of the distribution in field gradient has been developed. By this method average values of the field gradients were obtained. The results are almost equal to the values given in the earlier report. The source of this distribution; whether it lays in nonstoichiometry or not is now being investigated. In fig. 2 the temperature dependence of the line broadening and the separation at the angle 141
Volume
It
25
37A,
11
number
11
8
30
PHYSICS
2
11
‘1
1
35 TEMPERATURE
Fig. 2. Temperature the separation. Line
““““I
LETTERS
1971
Temperature was monitored fixing the ends of the two thermocouple directly to the sample. The transition temperature in fig. 2 was determined by the measurement of dielectric constant using the same sample used for the NMR experiment and the same thermocouple. The NMR data which show discontinuous jumps confirm to a high degree that the phase transition in AgNa(N02)a is of the first order. The thermal hysteresis [4] accompanied by the first order transition was not observed within our experimental accuracy. It can be partly due to the inhomogenity of the temperature (about 0.2O) which exists in the sample. The temperature dependence of the second order shift rotation pattern and the line width has been taken. This result and other details will be published elsewhere. 40
45
OC
dependence of the line width and width, as used here, is the sepa-
ration of the maxima of the derivative of the resonance. 3. 0: Line width at L~(c,H~) = 64’ for the b-rotation. Warming and cooling respectively. c1, W: Separation of the above line. Warming and cooling respectively. r\: Line width at a(c,Ho) = O” for the same rotation.
of 64 degrees which gives the largest separation for the b-rotation are shown. There is also given the temperature dependence of the line width at 0 degree, where the two components coalesce.
142
8 November
We would like to thank Dr. Y. Shiozaki for checking a single crystal by X-rays and Dr. M. Tokunaga for valuable discussions. Expenses were partly defrayed from the Science Research Grant of the Ministry of Education.
References
[l] M. Kasahara, T. Hikita and I. Tatsuzaki, J. Phys. Sot. Japan 29 (1970) 240. [2] L. Cavalca, M. Nardelli and A. Braibanti, Gazz. Chem. Ial. 83 (1953) 476. [3] M. E. Fitzgerald and P. A. Casabella, Phys. Rev. B2 (1970) 1350. [4] K.Gesi, J. Phys. Sot. Japan 28 (1970) 395.
PHYSICS
SPLITTING IN
OF THE 23 Na FERROELECTRIC
T. HIKITA, Research
Institute
LETTERS
of Applied
8 November 1971
NMR CENTRAL AgNa(N02)2
LINE
M. KASAHARA and I. TATSUZAKI Electricity,
Hokkaido
University,
Sapporo,
Japan
Received 11 September 1971 23 Splitting of the Na central line in AgNa(N02)2 was observed in the ferroelectric gradient-tensor in the ferroelectric phase and the paraelectric phase is discussed.
In a recent publication [l], the temperature dependence of the 23 Na quadrupole coupling constant (e2@/h) and the values of the principal components of the 23 Na electricfield-gradient tensor in the ferroelectric and paraelectric phase have been reported. Later, it was found that at certain angles of the b-rotation there is a remarkable line broadening in the ferroelectric phase. In order to obtain the correct shapes of the central line, the modulation amplitude was reduced as much as possible. It was revealed that the central line splits in the ferroelectric phase. The line shapes of the 23Na resonance in both phases are illustrated in fig. 1. This is not istent with the proposed space group DiE v [2]. It permits existence of two equivalent ? ield gradients with some restriction described below, resulting in the two central lines for the b-rotation. Each b-rotation pattern of the second order shift of the two 23Na central components in the ferroelectric phase has been obtained by calculating the separation of the two components. Since the splitting is not complete, the separation was calculated from the broadening. Line broadening versus separation has been computed by numerically superposing two Gaussian lines using a computer [3]. The two shift patterns are identical in sh&pe and symmetric with their symmetric points shifted from the origin about f 4 degrees, the average being the previously observed one. The a- and c-rotation patterns were also taken both in the ferroelectric and in the paraelectric phase. No splitting was observed for these rotations, and the line widths are almost temperature independent. These patterns are all symmetric about the angle at which the crystalline axis is parallel to the magnetic field. Thus we confirm that the principal axes coincide
phase. 23Na field-
Fig. 1. Line shapes of the (c, Ho) = 64’
(b I Ho).
23
Na resonance at ,X in the magnetic field 7100 G.
with the crystalline axes in the paraelectric phase. In the ferroelectric phase there exist two equivalent field gradients whose principal coordinate systems are rotated in the opposite directions to each other about 4 degrees from the crystalline axes around the b-axis. Though in such coordinate systems one rotation about a crystalline axis is sufficient to calculate the values of the principal components, calculation has been made for the three rotation patterns in both phases. Agreement is not gratifying. This seems to be due to the existence of the distribution in the field gradient. If the field gradient at Na differs from site to site, it would effect to the line and give considerable error to the calculation of the field gradient from the rotation pattern. A calculation method taking account of the distribution in field gradient has been developed. By this method average values of the field gradients were obtained. The results are almost equal to the values given in the earlier report. The source of this distribution; whether it lays in nonstoichiometry or not is now being investigated. In fig. 2 the temperature dependence of the line broadening and the separation at the angle 141
Volume
It
25
37A,
11
number
11
8
30
PHYSICS
2
11
‘1
1
35 TEMPERATURE
Fig. 2. Temperature the separation. Line
““““I
LETTERS
1971
Temperature was monitored fixing the ends of the two thermocouple directly to the sample. The transition temperature in fig. 2 was determined by the measurement of dielectric constant using the same sample used for the NMR experiment and the same thermocouple. The NMR data which show discontinuous jumps confirm to a high degree that the phase transition in AgNa(N02)a is of the first order. The thermal hysteresis [4] accompanied by the first order transition was not observed within our experimental accuracy. It can be partly due to the inhomogenity of the temperature (about 0.2O) which exists in the sample. The temperature dependence of the second order shift rotation pattern and the line width has been taken. This result and other details will be published elsewhere. 40
45
OC
dependence of the line width and width, as used here, is the sepa-
ration of the maxima of the derivative of the resonance. 3. 0: Line width at L~(c,H~) = 64’ for the b-rotation. Warming and cooling respectively. c1, W: Separation of the above line. Warming and cooling respectively. r\: Line width at a(c,Ho) = O” for the same rotation.
of 64 degrees which gives the largest separation for the b-rotation are shown. There is also given the temperature dependence of the line width at 0 degree, where the two components coalesce.
142
8 November
We would like to thank Dr. Y. Shiozaki for checking a single crystal by X-rays and Dr. M. Tokunaga for valuable discussions. Expenses were partly defrayed from the Science Research Grant of the Ministry of Education.
References
[l] M. Kasahara, T. Hikita and I. Tatsuzaki, J. Phys. Sot. Japan 29 (1970) 240. [2] L. Cavalca, M. Nardelli and A. Braibanti, Gazz. Chem. Ial. 83 (1953) 476. [3] M. E. Fitzgerald and P. A. Casabella, Phys. Rev. B2 (1970) 1350. [4] K.Gesi, J. Phys. Sot. Japan 28 (1970) 395.