著者

Kei-ichiro Murai Koyumi Yamashita Ginga Kitahara Makoto Tokuda Akira Yoshiasa

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.220901, (Released:2023-03-11)

被引用文献数

2

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Single crystals of CaW1-xMoxO4 scheelite-powellite solid solutions (x= 0.0, 0.03, 0.08, 0.2, 0.3, 0.5, 0.8 and 1.0) were synthesized using a melting method. The light emission spectra of the solid solutions were measured using a JASCO FP-8300 fluorescence spectrometer. The maximum fluorescence peak at 419 nm in the CaWO4 scheelite end-member greatly decreases in intensity and shifts its peak position to 451 nm with only 3% Mo substitution. The change in near-ultraviolet light emission intensity at 292 and 301 nm are more moderate than those in the strong peak at 419 nm. The tendency of change in intensity and wavelength shift due to the Mo substitution differs among these fluorescence peaks. Single crystal X-ray diffraction experiments for the CaW1-xMoxO4 solid solutions (x= 0.0, 0.2, 0.3, 0.5, 0.8 and 1.0) were carried out using a Rigaku Super-Nova Single source at offset/far HyPix3000 diffractometer. The R1 index for CaW1-xMoxO4 solid solutions were convergent to 1.22 -1.71% using anisotropic temperature factors. The expansion of the c-axis and shrinkage of the unit cell volume were induced with an increase in Mo content. The significant increase in the angle ∡Ocloser-Ca-Ocloser was directly related to the expansion of the c-axis. The Debye temperature ΘD for Ca, W and O atoms in CaWO4 were 381, 198 and 534 K, respectively. The obtained ΘD for Ca, Mo and O atoms in CaMoO4 were 363, 257 and 503 K, respectively. The phonon density of states estimated from the lattice dynamics calculations coincided with the observed ΘD values.

著者

Hidetomo HONGU Akira YOSHIASA Ginga KITAHARA Yumiko MIYANO Karin HAN Koichi MOMMA Ritsuro MIYAWAKI Makoto TOKUDA Kazumasa SUGIYAMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.200904, (Released:2021-09-30)

被引用文献数

2

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Parasymplesite and vivianite specimens were obtained from Kiura Mine, Ohita, Japan and Tomigaoka, Nara, Japan, respectively. Empirical chemical formulas of the specimens determined by energy–dispersive X–ray spectroscopy on the scanning electron microscopy were Fe3(AsO4)2·8H2O, and (Fe0.93Mn0.06Mg0.01)3(PO4)2·8H2O, respectively. The crystal structures of parasymplesite and vivianite determined by single–crystal X–ray diffraction method were monoclinic, space group C2/m, with unit–cell parameters: a = 10.3519(10), b = 13.6009(13), c = 4.7998(4) Å, β = 104.816(2)°, V = 653.32(11) Å3 (Z = 4), and monoclinic, space group C2/m, with unit–cell parameters: a = 10.1518(6), b = 13.4327(7), c = 4.7005(3) Å, β = 104.692(2)°, V = 620.03(6) Å3 (Z = 4), respectively. The crystal structure of parasymplesite solved with the ideal chemical formula was refined to the R1 value of 0.0301 (wR2 = 0.0788) for 722 independent reflections with |Fo| > 4σ(|Fo|), whereas that of vivianite was refined to the R1 value of 0.0272 (wR2 = 0.0832) for 664 independent reflections. The hydrogen atom positions determined by the difference Fourier method coincided with the positions where residual electron density peaks appeared. In the edge–sharing Fe2O6(H2O)4 double octahedra in parasymplesite and vivianite, the bond distance of Fe2–O5, where O5 is the oxygen atom of the H2O molecule, is shorter than that of Fe2–O2. In each arsenate and phosphate phase, only the M2–O2 bond distance shows an increase trend with the increase in the average ionic radii of the M2 site, but the M2–O3 bond distance never shows a clear average M2 ionic radius dependence. In vivianite group minerals, a distortion at the isolated M1O2(H2O)4 octahedra increases as a function of the average M1 ionic radius. The respective complex sheets consisting of the TO4 tetrahedra, isolated M1 octahedra, and edge–sharing M2 double octahedra are connected only by the hydrogen bond O5–H52•••O4. In the arsenate phases, the donor–acceptor distance between O5 and O4 exhibits an increase trend as increase of the average M ionic radius, but in the phosphate phases, there is no clear correlation between donor–acceptor distances and the average M ionic radius.

著者

Ginga KITAHARA Akira YOSHIASA Makoto TOKUDA Tsubasa TOBASE Kazumasa SUGIYAMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.116, no.1, pp.45-55, 2021 (Released:2021-03-06)

参考文献数

43

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Structural analysis of Ce– and Nb–perovskites containing Fe, Zr, Nb, and rare earth elements (REEs) in CaTiO3 perovskite was performed using single–crystal X–ray diffraction and X–ray absorption near–edge structure (XANES) analyses. Based on chemical analysis results, XANES measurements and the site–occupation of elements at A– and B–sites showed the chemical formula:(Ca2+0.817REE3+0.087Na+0.081Sr2+0.005Th4+0.003)1.998+0.993(Ti4+0.941Nb5+0.017Fe3+0.013V5+0.010Fe2+0.007Sc3+0.006Zn2+0.005Al3+0.002Ge4+0.001W6+0.001)3.996+1.003O3 for Ce–perovskite and(Ca2+0.937Ce3+0.021Na+0.020La3+0.015Sr2+0.003)2.008+0.996(Ti4+0.730Nb5+0.122Fe3+0.108Al3+0.020Zr4+0.009V5+0.008)3.990+0.997O3for Nb–perovskite. In Ce– and Nb–perovskites, the total charges at the A– and B–sites achieved near–ideal divalent and tetravalent states such as Ca2+Ti4+O3, respectively, due to complex elemental substitutions. Local distortions around Ti in the perovskite solid solutions were greater, and the pre–edge features of the Ti atoms in Ce– and Nb–perovskites were different from those in pure CaTiO3. The valence states and local structures of Fe in Ce– and Nb–perovskites were significantly different. The existence of divalent Fe2+ at the B–site in Ce–perovskite was confirmed. It is presumed that the displacement ellipsoids of all atoms and local irregularities in Ce–perovskite increase owing to the radiative decay of the actinoid element Th. We reconfirmed that the composition and three–dimensional structure of perovskite–type structures were flexible and caused various electrical, structural changes.