Masaru Kasahara

Raman spectral of low-lying longitudinal mode of KH2PO4 and KD2PO4 in ferroelectric phase

Abstract The origin of the low-lying modes of KH 2 PO 4 and KD 2 PO 4 in the ferroelectric phase has been clarified by the z(xy)z Raman scattering experiments. The “ S -mode”, which has been usually assigned to the proton tunneling mode in KH 2 PO 4 at T T c , has been found in the z(xy)z spectrum of KD 2 PO 4 in contrast to the x(xy)y spectrum. It has been found that the frequency of the “ S -mode” of KD 2 PO 4 is higher than that of KH 2 PO 4 . These results have shown that the “ S -mode” is far from the proton tunneling mode nor the proton/deuteron mode at all. From the present Raman spectroscopy, it is concluded that the “ S -mode” is assigned to the libration mode of the PO 4 tertahedrons.

Light Scattering by the Polarization Fluctuation in the Low Concentration Region of DKDP in Mixed Crystals KDP1-xDKDPx

Light scattering spectra of mixed crystals KDP 1- x DKDP x with x =0.08, 0.04 and 0.0 (KDP) are measured by a Fabry-Perot interferometer with a free spectral range of 8 cm -1 . Spectra are analyzed with the Debye type susceptibility of a polarization fluctuation coupled to an acoustic phonon. The relaxation times of an isolated dipole for x =0.08, 0.04 and 0.0 are found to be 0.27, 0.21 and 0.15 in the unit of 10 -12 sec, respectively.

Spin-Lattice Relaxation Time of Proton in (NH4)2SO4–K2SO4 Mixed Crystals

The temperature dependence of the proton spin-lattice relaxation time T 1 of [(NH 4 ) 1- x K x ] 2 SO 4 was studied. As the concentration of K 2 SO 4 , x increases, it is found that (1) the temperatures of two T 1 minima shift downwards, (2) T 1 versus 1/ T curves become broader near each T 1 minimum and (3) T 1 at the right minimum is longer than that at the left minimum for x ≤0.19. The experimental result (3) may suggest that more K + ions are substituted for NH 4 + (I) than for NH 4 + (II) ions. A single T 1 minimum curve is obtained for x =0.84. This means that only one type of NH 4 + ions, NH 4 + (II), remains at higher concentration of K 2 SO 4 .

Deuteron Magnetic Resonance in KD3(SeO3)2

Quadrupole coupling constant and the direction of the principal axes of EFG tensor of deuterons in KD 3 (SeO 3 ) 2 are obtained from 40 to –106°C. It is confirmed that there exist two symmetrically inequivalent deuterons D(1) and D(2), and D(1) is ordered in the disordered phase. Deuterons D(2) are found to be dynamically disordered in the disordered phase. In the ordered phase, D(1) sites are divided into two inequivalent groups while the number of D(2) sites remains unchanged. The splitting of the resonance line of D(1) in the ordered phase depends on temperature as ( T tr - T ) β , where T tr is 24.9°C and β is about 0.52±0.08 in the temperature from 24.4 to 22°C and 0.46±0.01 from 22 to 3°C. The relation between the splitting and the order parameter is discussed.

Raman Scattering Study of SrTi18O3

Antiferrodistortive and ferroelectric soft modes of isotoped ferroelectric SrTi 18 O 3 x 16 O 3(1- x ) were observed for a single crystal of x =0.87 with Raman scattering. The frequency of one of t...

Raman Scattering Study of the Soft Mode in Ferroelectric (CH3NHCH2COOH)3CaCl2

Raman spectra of the soft modes have been measured in the very vicinity of the transition temperature T c =131.7 K in the ferroelectric phase of (CH 3 NHCH 2 COOH) 3 CaCl 2 (TSCC) with scattering geometries b - c ( b + c , b - c ) b + c and c - b ( c + b , c - b ) c + b . The longitudinal soft mode is still o bserved as an underdamped mode even just below T c , whereas the transverse one is overdamped. The temperature dependence of dielectric constant described with the small Curie-Weiss constant is quantitatively explained by those of the two modes in terms of the Lyddane-Sachs-Teller relation. The effective relaxation time of the overdamped mode is the same order of magnitude as the relaxation time obtained by dielectric dispersion. The temperature dependence of the intensity of the soft mode agrees with the theoretical prediction based on the fact that this mode becomes Raman active below T c .

Scattering Angle Dependence of Brillouin Shift near the Normal-Incommensurate Phase Transition Point of Rb2ZnCl4

Brillouin shifts of the C 11 mode were measured near the normal-incommensurate phase transition temperature with two scattering angles: 90 and 45 degrees. The scattering angle dependence of the Brillouin shifts is found and is inferred to be caused by the fluctuation of an order parameter.

23Na Nuclear-Magnetic-Resonance Study of the Ferroelectric Transition in Silver Sodium Dinitrite, AgNa(NO2)2

The central NMR spectrum of 23 Na in the ferroelectric silver sodium dinitrite (AgNa(NO 2 ) 2 ) is investigated. The second-order quadrupolar-shifts in the single crystals are measured. The rotation patterns about the three crystalline axes in the paraelectric and the ferroelectric phases are analysed by Volkoff method. For the calculation of the EFG, the chemical shift of 23 Na ions as well as the distribution in the EFG must be taken into account. The 23 Na EFG tensors in a unit cell of AgNa(NO 2 ) 2 are identical in the paraelectric phase. The split into the two kinds of EFG whose principal components are equal in magnitude and differ only in the orientation of the principal axes. The powdered samples show that nonstoichiometry does not affect the electric field gradient seriously. The temperature dependence of the EFG tensor is discussed in comparison with that of NaNO 2 .

Raman Scattering Study on the Phase Transition of NH4H2PO4 and ND4D2PO4

Raman scattering spectra of NH 4 H 2 PO 4 and ND 4 D 2 PO 4 are studied in the paraelectric and antiferroelectric phases to determine the site symmetries of H 2 PO 4 - (D 2 PO 4 - ) and NH 4 + (ND 4 + ) ions. The site symmetries of both ions are found to be C 1 in the antiferroelectric phase in accordance with the Nagamiya model. On the other hand, any evidence of the local C 1 symmetry is not found in the spectra above the transition temperature and the site symmetries of these ions are determined to be C 2 . These experimental results are discussed in relation to the validity of the Slater type model.

Deuteron Magnetic Resonance in RbD3(SeO3)2

Deuteron magnetic resonance study of RbD 3 (SeO 3 ) 2 was made between -165 and 14°C. Electric quadrupole coupling constants and directions of the principal axes of EFG tensors were obtained in the paraelectric phase. There are three types of hydrogen bonds with different behavior which play some roles at phase transition. The relation between the temperature dependence of the resonance spectra and that of doubly degenerate soft-mode is discussed.