Raman Scattering Investigation of Structural Transition in Ca5Ir3O12

We report a study of the second-order phase transition at 105 K in the geometrically frustrated iridate Ca5Ir3O12 using a Raman scattering method. The Raman scattering spectra of a single crystal were measured from 4 K to room temperature. Ab initio phonon calculations that consider the spin–orbit interaction were also conducted and compared with the experimental spectra. Agreement between the theoretical and experimental results at room temperature is reasonably good. At room temperature, 6A\u271+9E\u27+5E\u27\u27 were assigned among the Raman active modes, 6A\u271+13E\u27+6E\u27\u27, based on the reported P6¯2m crystal structure. Below Ts, 23 additional peaks were observed, suggesting the appearance of a superlattice structure. The polarization dependence of Raman spectra below Ts indicates the existence of 6¯ symmetry. We observed at least one additional mode as a broad weak-intensity peak at temperatures higher than Ts. This suggests possible local distortion around the Ir ions, which would be expected for Ir ions with mixed valence states

Off-center rattling and cage vibration of the carrier-tuned type-I clathrate Ba_8Ga_16Ge_30 studied by Raman scattering

To reveal dynamical property of a guest ion in type-I clathrate compound, n-and p-type clathrates Ba8Ga16Ge30 have been investigated by Raman scattering. It is found that the guest ion in a 6d-site cage (6d-cage) rotationally moves for both n-and p-type since the additional guest mode Eg(A) has been observed regardless of its carrier. The potential-energy difference between [100] and [110] directions in the 6d-cage is proportional to the off-center distance of the guest-ion position from the cage center and this off-center distance for p-type is much larger than that for n-type Ba8Ga16Ge30. In addition, the Raman intensity of the cage vibration at a 6c site for p-type is weaker than that for n-type. Thus, the amplitude of the vibration at the 6c site becomes small for p-type, and this small amplitude induces a large movable space for the guest ion, i.e., this vibrational amplitude of the 6c-site atom works as the barrier for the off-center position. For both systems, the guest ion in the 6d-cage shows an anharmonic vibration, judging from the anomalous energy decrease in the guest ion with decreasing temperature. The energy difference between T-2g and T-1u [T. Mori et al., Phys. Rev. B 79, 212301 (2009)] of the guest mode clearly supports the theoretical prediction of an interacting dipoles picture that explains the glasslike properties of the off-centered clathrate. It is concluded that the off-center rattling plays an important role to suppress a lattice thermal conductivity

Spatiotemporal Analysis of the Molecular Interaction between PICK1 and PKC

PICK1 is a protein which was initially identified as a protein kinase Cα (αPKC) binding protein using the yeast two-hybrid system. In addition to αPKC, the PICK1 complex binds to and regulates various transmembrane proteins including receptors and transporters. However, it has not been clarified when and where PICK1 binds to αPKC. We examined the spatio­temporal interaction of PICK1 and PKC using live imaging techniques and showed that the activated αPKC binds to PICK1 and transports it to the plasma membrane. Although the membrane translocation of PICK1 requires the activation of αPKC, PICK1 is retained on the membrane even after PKC moves back to the cytosol. These results suggest that the interaction between αPKC and PICK1 is transient and may not be necessary for the regulation of receptors/transporters by PICK1 or by αPKC on the membrane

The anharmonic vibration of Li in lithium amide

A large amplitude rattling-type anharmonic vibration of Li is possible without guest-host type structure, as we report here for tetragonal LiNH2 crystal. The low temperature (0.4–300 K) specific heat capacity and Raman spectroscopy support the phonon model of site-specific Li activities governed by the symmetry of the potential energy distribution around the Li atoms in LiNH2, which yields the anharmonic Li3 vibration (optical) in one direction (either X or Y axis of the crystal), while the Li1 and Li2 atoms remain silent. Our finding may help to correlate ionic conductivity, thermal, and hydrogenation properties of LiNH2

Regular-Triangle Trimer and Charge Order Preserving the Anderson Condition in the Pyrochlore Structure of CsW2_2O6_6

Since the discovery of the Verwey transition in magnetite, transition metal compounds with pyrochlore structures have been intensively studied as a platform for realizing remarkable electronic phase transitions. We report the discovery of a unique phase transition that preserves the cubic symmetry of the beta-pyrochlore oxide CsW$_2$O$_6$, where each of W 5d electrons are confined in regular-triangle W3 trimers. This trimer formation is an unprecedented self-organization of d electrons, which can be resolved into a charge order satisfying the Anderson condition in a nontrivial way, orbital order caused by the distortion of WO6 octahedra, and the formation of a spin-singlet pair in a regular-triangle trimer. Electronic instability due to the unusual three-dimensional nesting of Fermi surfaces and the localized nature of the 5d electrons characteristic of the pyrochlore oxides were found to play important roles in this unique charge-orbital-spin coupled phenomenon.Comment: 7 pages, 3 figure

Raman scattering investigation of filled skutterudite PrRu4P12

Raman scattering spectra of the single crystalline PrRu4P12 have been measured in the temperature region between 1.5 K and 300 K. Below TMI, new peaks appear at phonon region and these peaks are assigned as the Raman-active phonons with Pm^3 symmetry. While, the broad spectra in the lower energy region than 200cm.1 become sharp below TMI and the detailed polarization measurements conclude that these are the crystal field excitations(CF) due to two-different Pr sites. Furthermore, temperature dependence of the CF energy levels for Pr2 has been clarified.Raman scattering spectra of the single crystalline PrRu4P12 have been measured in the temperature region between 1.5 K and 300 K. Below TMI, new peaks appear at phonon region and these peaks are assigned as the Raman-active phonons with Pm3 symmetry. While, the broad spectra in the lower energy region than 200cm-1 become sharp below TMI and the detailed polarization measurements conclude that these are the crystal field excitations(CF) due to two-different Pr sites. Furthermore, temperature dependence of the CF energy levels for Pr2 has been clarified

Quantitative estimation of NH3 partial pressure in H2 desorbed from the Li-N-H system by Raman spectroscopy

The partial pressure of NH3 gas estimated by Raman spectroscopy indicates that ~0.1% NH3 is inevitably contaminated in H2 desorbed from the hydrogen storage material composed of LiH and LiNH2 at any temperatures up to 400 °C in a closed system

Raman scattering investigation of Y1-xCaxTiO3

Raman scattering spectra of single crystalline Y12xCaxTiO3 (x=0, 0.10, 0.30, 0.37, 0.38, and 0.41) have been systematically studied in the temperature region from 298 to 8 K. The structural transition from the orthorhombic phase to the monoclinic one occurs below 200 K in x<0.38. The intensity increase, related to the metal-insulator transition, has been observed below 100 K in Y0.62Ca0.38TiO3 . The phase separation from the monoclinic phase to the metallic orthorhombic and insulating monoclinic phase occurs below the metalinsulator transition temperature (TMI) in Y0.62Ca0.38TiO3 . The intensity-increase is explained by the appearance of the orthorhombic structure below TMI and its anisotropic appearance is related to the random orientation of the principle axes of the orthorhombic grain