We observed quasi-elastic light scattering (QELS) in BiFeO3 using Raman spectroscopy over a temperature range of 300-860 K. The QELS has two components: a narrow and broad component. The temperature dependence of the intensity and linewidth of the broad component differed below and beyond the Néel point, and the broad QELS may have a magnetic origin.

To understand the origin of the nitrate anion selectivity in layered double hydroxide (LDH; [Ni1−xAlx(OH)2]Clx) materials (i.e., Cl−-NiAl(x)LDH; x = 1/3 and 1/5) comprising Ni2+, Al3+, and exchangeable chloride anions, the equilibrium and kinetic properties of the chloride-to-nitrate anion exchange reaction were investigated in aqueous media. The anion exchange isotherms of the studied systems showed that the nitrate anion selectivity was significantly higher at x = 1/5 than at x = 1/3. The fine crystal structures of the LDH materials and the hydration states of the nitrate anions in their interlayer spaces were identified by synchrotron-radiation X-ray diffraction (SXRD) and Raman spectroscopy, respectively. The nitrate anion selectivities of Cl−-NiAl(x)LDH (x = 1/3 and 1/5) were determined by the relationship between the magnitudes of the thermal vibration parameters of the chloride and nitrate anions; the anion exchange reaction primarily gave NiAl(x)LDH containing anions with smaller thermal vibration parameters. Time-resolved SXRD measurements of the anion exchange reaction revealed that the exchange pathway differed depending on the nitrate anion selectivity. The nitrate anion removal ability and selectivity of Cl−-NiAl(x)LDH (x = 1/3 and 1/5) in artificial seawater were maintained, suggesting that Cl−-NiAl(1/5)LDH could be used for nitrate removal from contaminated seawater.

We measured light scattering in a single crystal of ZrW2O8 (ZWO) in the frequency range between 0.1 and 1100 cm−1 and in the temperature range between 3.5 and 300 K. From the temperature dependence of the optical and acoustic phonon frequencies, we found that low-frequency phonon modes below 100 cm−1 have large relative temperature coefficients (total anharmonicity values). The longitudinal acoustic mode, whose Brillouin light scattering has not been reported thus far, was found to have the largest negative total anharmonicity in a wide temperature range, indicating the possibility that the acoustic modes, as well as the low-frequency optical modes that are associated with the motions of WO4 and ZrO6 polyhedra, should contribute to the negative thermal expansion of ZWO.

We performed Brillouin light scattering spectroscopy on a single crystal of BiFeO_3 (BFO) in the temperature range from 110 K to 300 K and observed the Brillouin scattering from the longitudinal acoustic (LA) and transverse acoustic (TA) phonon modes, which were traveling along the c-axis. We determined the elastic constants for the LA mode (C_33) and TA mode (C_44) to be approximately 251 GPa and 90.3~103 GPa at 300 K, respectively. We observed splitting of the degenerate TA modes (corresponding to the elastic constant C_44), which is not expected for the TA modes traveling along the three-fold symmetry axis (the c-axis) of BFO. We also present the temperature dependences of the frequencies of the LA and TA modes, which include anomalies such as the LA mode softening and TA mode frequency drop at around 210 K.