Powder X-ray diffractometry (XRD) and Raman scattering measurements were used to study the structural changes of compositionally homogeneous metastable ZrO 2 solid solutions induced by ScO 1.5 doping. The crystal structures of monoclinic, tetragonal, cubic, and rhombohedral (Sc 2 Zr 7 O 17 , ␤-phase) solid-solution phases have been refined by using the Rietveld analysis of the XRD data at room temperature of arc-melted ZrO 2 -XScO 1.5 (X = 0, 2, . . . , 20, and 22 mol%) samples. The results can be interpreted as indicating that the structures of the monoclinic and tetragonal phases approach those of the tetragonal and cubic phases, respectively, by ScO 1.5 doping. Raman scattering, as well as XRD, was useful to investigate the phase assemblage. Moreover, we could obtain Raman spectra of the ␤-phase probably for the first time.

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Calcium hydroxyapatite (HAp, Ca 10 (PO 4 ) 6 (OH) 2 ) is the principal inorganic component of bone and teeth, bioactive material, and proton (H + ) conductor. However, the chemical bonding and structural disorder of HAp are unclear. Here we report precise chargeand nuclear-density distributions of HAp at 298 and 673 K. The present results clearly demonstrate the covalent PÀO and OÀH bonds, more ionic CaÀO bonds, and the charge transfers from P to O atoms and from H to O atoms in HAp. This work shows that the hexagonalÀmonoclinic phase transition of HAp is accompanied by the occupational and orientational ordering of OH À ions, the tilting of the PO 4 tetrahedron, and the Ca displacements. Diffusion paths of proton are visualized along the c-axis in hexagonal HAp. We anticipate that the visualization of chemical bonding and structural disorder of HAp will contribute greatly to our understanding of biominerals, reactions, biological organisms, and the diffusion process in HAp-based proton conductors.

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We present the results of experiments that assess the viability of anti-Stokes scattering to investigate in situ materials at high temperatures. Both anti-Stokes and Stokes Raman measurements have been performed at various high temperatures using hafnia as a test material. As compared with Stokes Raman spectra, anti-Stokes spectra were observed with lower thermal emission backgrounds in accordance with Planck’s equation. The intensity ratio of anti-Stokes to Stokes scattering approaches 1 as the temperature increases at high temperatures satisfying the Boltzmann distribution law. These results clearly demonstrate the advantage and feasibility of anti-Stokes Raman scattering for the elimination of the thermal emission in comparison with Stokes scattering.

Differential scanning calorimetry and Raman spectroscopy measurements have been performed to investigate the β-cubic (c) phase transition of the compositionally homogeneous ZrO2-22 mol % ScO1.5 solid solution. The enthalpy of transition (1.11 kJ/mol of cation) and thermal hysteresis between β- and c-phases were smaller than those between monoclinic (m) and tetragonal (t) phases of ZrO2, reflecting the structural information that the cell volume ratio of β- to c-phases is smaller than that of m- to t-phases. Raman spectroscopy allowed us to observe the β-c phase transition, and we could obtain Raman spectra of the c-phase in the ZrO2–ScO1.5 system. This result was strongly supported by the observation of x-ray diffraction patterns at high temperatures.

Calcium hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is the principal inorganic component of bone and teeth, one of the most important bioceramics, and a proton (H+) conductor with potential for energy conversion devices. The proton diffusion pathway in the HAp lattice is a key to understand the proton conduction mechanism and chemical reaction. Previous neutron-diffraction studies of HAp visualized the short-range proton diffusion pathway. In this work, we report the successful visualization of the long-range proton diffusion pathway in stoichiometric HAp at 923, 673, and 298 K through a combined technique of high-temperature neutron diffraction and bond valence method. We have visualized (1) one-dimensional proton diffusional pathways along the c-axis in the hexagonal channel and (2) two-dimensional proton migration pathway network on the ab-planes at z = 0 and 1/2. The proton diffusion and reorientation of hydroxide ions (OH–) are a complex sinusoidal process in the hexagonal channel along the c-axis, which is consistent with the anisotropic nuclear-density distribution of proton obtained by the neutron diffraction and maximum-entropy method.