Yuhji Tsujimi

Brillouin scattering study on relaxor ferroelectric Pb(Zn1/3Nb2/3)O3

The 90° Brillouin scattering experiment has been performed on a Pb(Zn1/3Nb2/3)O3 single crystal. The frequency shift and linewidth of the c33 pure longitudinal acoustic mode and the c44 pure transverse mode show bending anomalies near Tm=397 K, at which the low-frequency dielectric constant e has a maximum value. In addition to the acoustic modes, a relaxational mode is found in the form of a central peak. The relaxation time τ of the mode has a temperature dependence similar to that of e and shows a broad peak anomaly around Tm. The temperature dependence of τ can be analyzed by a modified superparaelectric model.

Dynamical slowing down of polar nanoregion in relaxor-based ferroelctric 0.89Pb(Zn2∕3Nb1∕3)O3–0.11PbTiO3

Light scattering experiment has been performed in a single crystal of 0.89Pb(Zn1∕3Nb2∕3)O3–0.11PbTiO3. The central peak (CP) spectra have been well detected with high resolution over the wide frequency region up to 150GHz. The distribution is discovered in the relaxation time associated with the CP. Moreover, it is found that the maximum relaxation time indicates the dynamical slowing down near the temperature Tm at which the low-frequency dielectric constant has a maximum. This finding strongly suggests that the physical origin of the CP is “polar nanoregions.”

Brillouin Scattering Study of the Anisotropic Relaxation of the Polarization Fluctuation in Ferroelectric TGS

The polarization relaxation phenomena in the uniaxial ferroelectric TGS have been studied by the observation of the angular dependence of the Brillouin scattering spectra. Both the frequency shift and the full width of the Brillouin satellite show remarkable anisotropic anomalies most strongly at 44.94°C below the transition temperature T c =48.86°C. The experimental result is successfully interpreted from the viewpoint of the depolarization effect on the polarization fluctuation. The effect is characterized by the anisotropic relaxation time with only two parameters ; a relaxation time τ 0 for a transverse polarization fluctuation and a generalized Lorentz factor L . The values τ 0 =(0.93±0.09)×10 -11 sec and L ≃0.41 give a good description of the experimental result.

Brillouin and Raman scattering study of the isotopically induced ferroelectric phase transition of SrTi18O3

The ferroelectric phase transition of the isotope 18 O exchanged strontium titanate SrTi 18 O 3 has been studied by both Brillouin- and Raman scattering near T m where the dielectric constant takes a maximum value. The Brillouin scattering study elucidates anomalous temperature dependence of the acoustic modes; the c 44 mode shows a drastic softening though the c 33 mode is almost independent of temperature. The Raman scattering study below T m shows a weak softening behavior of the ferroelectric mode. Existence of the ferroelectric micro-region is suggested in the isotopically induced ferroelectricity of SrTi 18 O 3 .

A single exponential time decay of the ferroelectric soft B2 mode of KDP studied by impulsive stimulated Raman scattering

Abstract The ferroelectric soft modes of KDP (KH2PO4) and the 90% deuterated compound (K(H0.1D0.9)2PO4) have been excited coherently by impulsive stimulated Raman scattering. The observed time dependence of the excited modes shows a complete single exponential time decay after an electronic response at its time origin. The temperature dependence of the relaxation time τ of the modes shows clearly a critical slowing down in paraelectric phase, τ = τ 0 T 0 (T−T 0 ) , where T0 is the phase transition point of the clamped crystal. The isotope effect on τ is well confirmed as τ0 is 0.11×10−12s for KDP and τ0 is 0.82×10−12s for K(H0.1D0.9)2PO4.

Ferroelectric phase transition of SrTi18O3 studied by brillouin scattering

Abstract Ferroelectric phase transition of SrTi18O3 (87% 18O-exchanged SrTiO3) has been investigated by the 90° Brillouin scattering experiment in the VV and VH scattering geometries. The c 44 pure transverse acoustic mode splits into two modes below T c≈25 K, indicating that the phase transition takes place (or begins) at T c and that the phase realized below T c has lower crystal symmetry than tetragonal one.

Frequency and time-resolved spectroscopic study of liquid–glass transition in D-sorbitol

The two-step relaxation (α and β relaxations) in D-sorbitol has been successfully investigated in a wide frequency range of about 8 decades from 200 kHz to 10 THz by three types of light scattering techniques; Raman and Brillouin scatterings (0.2 GHz–10 THz) and time-resolved spectroscopy (200 kHz–1 GHz). A remarkable result is that a relaxation time of the α relaxation shows a critical behavior not at the liquid–glass transition temperature Tg=−7°C but at the ergodic to nonergodic transition temperature Tc=36±2°C.

Coherent Excitation of Ferroelectric Soft B2 Mode of KDP by Impulsive Stimulated Raman Scattering.

Coherent excitation of the ferroelectric soft modes of KDP has been done in the time domain by femtosecond impulsive stimulated Raman scattering. The observed time dependence shows clearly a relaxational character of the soft mode in a wide temperature range above T c . A critical slowing-down is directly revealed in the temperature dependence of the relaxation time τ= τ 0 T 0 /( T - T 0 ) as τ 0 is 0.11 ×10 -12 s, where T 0 is the phase transition point of the clamped crystal. The order-disorder phase transition mechanism is reasonable within the limit of the time resolution of the present study.

Brillouin scattering of the order-disorder type phase transition in NaNO3

Abstract NaNO3 undergoes the order-disorder type phase transition with the anti-parallel order of NO3 molecules along the three-fold z axis at Tc = 276.5°C. A Brillouin scattering experiment was performed to observe the c33 pure longitudinal acoustic mode coupled with the fluctuation of the anti-parallel order in the temperature range between 23.22°C and 299.55°C. The relaxation time of the fluctuation was determined as a function of temperature below Tc to be τf/(Tc − T), where τfis(6.0 ± 0.7) × 10−11s deg. τf is one order lower than the previous result reported by the ultrasonic study.

Impulsive Stimulated Brillouin Scattering Study on the Relaxation of the Polarization Fluctuation in Ferroelectric TGS

The quasi c 33 acoustic mode of ferroelectric TGS is observed by impulsive stimulated Brillouin scattering. The mode is excited by picosecond laser pulses at 500 MHz and 2.0 GHz and its vibrational behavior is probed in real time. The temperature dependence of the velocity of the mode shows an anomaly through a piezoelectric coupling with the fluctuating polarization below the transition temperature T c . The relaxation time τ 0 of the order of 10 -10 s· deg is obtained which is longer than these reported in the previous Brillouin scattering and the ultrasonic studies.