K. Uheda

Synthesis of Gd1 − x Eu x Al3 ( BO 3 ) 4 ( 0 < x ⩽ 1 ) and Its Photoluminescence Properties under UV and Vacuum Ultraviolet Regions

Single phase europium-activated gadolinium aluminum borate, Gd 1 x Eu x Al 3 (BO 3 ) 4 (0 ≤ x ≤ 1) was obtained by the evaporation of its nitrate solution, and calcination at 900 to 1100°C in air. All the solid solution was identified as the isomorphs of huntite. Eu 3+ activated GdAl 3 (BO 3 ) 4 showed intense red emission with CIE chromaticity coordinates of (0.645, 0.330) under 147 nm excitation. According to the excitation and emission spectra, the red emission of Eu 3+ was decreased under excitation of the vacuum ultraviolet (VUV) region (158-160 nm), and increased under excitation UV region (258-260 nm) with the increase of Eu 3+ concentration. In comparison with the absorption data of borates, the 158 nm excitation peak was assigned to the energy level of BO 3 groups. In excitation spectra, the sharp 274 nm peak, corresponding to the 8 S 72 → 6 I 2/11 transition of Gd 3+ in addition to the f-f transitions of Eu 3+ were observed. Consequently, the emission of Eu was induced by the energy transfer of VUV excitation to the activator Eu 3+ ions via the co-activator Gd 3+ in GdAl 3 (BO 3 ) 4 .

A new ferromagnetic polymorph of CrSb2 synthesized under high pressure

Abstract A new ferromagnetic polymorph of CrSb 2 was synthesized under high-pressure–temperature conditions. The crystal structure is body-centered tetragonal with the space group I 4/ mcm , namely the CuAl 2 -type structure. The experiments under various pressure conditions revealed that the high-pressure polymorph was formed above 5.5 GPa, and the compound crystallized into the low-pressure marcasite-type structure below 5 GPa. The characteristic of the high-pressure phase is the metallic bond nature including the formation of Cr–Cr–Cr linear chain along the c -axis. The compound shows metallic conductivity and itinerant-electron ferromagnetic behavior with the Curie temperature of 160 K.

High-pressure synthesis of ferromagnetic Mn3Ge with the Cu3Au-type structure

A new intermetallic compound, Mn3Ge, has been synthesized by direct reaction of elemental components at 6.2 GPa and 1000°C for 30 min using a belt-type high-pressure apparatus. The compound crystallizes into a cubic structure with the space group Pm3m, namely the L12-type (Cu3Au-type) structure. The structure was refined by Rietveld analysis of the powder x-ray diffraction data and the lattice constant was determined as a = 0.380 19(3) nm. The compound shows metallic conductivity and ferromagnetism with a Curie temperature of 400 K.

High Pressure Crystal Chemistry of Transition Metal Diantimonides

High-pressure crystal chemistry of transition metal diantimonides is discussed. Two types of pressure-induced phase transitions, marcasite-type to CuAl2-type and marcasite-type to pararammelsbergite-type, occur in this family. The former is found in CrSb2 and the transition is accompanied by a change in bonding character from the mixed ionic and covalent to metallic. The latter is found in NiSb2 and can be explained by effective packing of NiSb6 octahedra. The local environment of nickel atom remains unchanged during the transition. The phase transition sequences in transition metal diantimonides, together with other dipnictides and dichalcogenides, are schematically summarized.

High Pressure Synthesis of Binary B–S Compounds

r-BS was synthesized under high pressure/temperature conditions. Rietveld analysis of the powder X-ray diffraction data was performed by applying the structure model of GaS 3R (space group: R3m) with the lattice parameters of ahex = 3.05223(7) A and chex = 20.4119(5) A The crystal structure of r-BS was revealed to be the three-layer structure comprised of the units built up from B–B pairs which are inside the anti-prism of S atoms. The measurement of UV-Vis diffused reflectance spectrum showed that the estimated band gap of r-BS was about 3.4 eV, and the coloring of r-BS was observed as broad absorption at 510 nm.

Synthesis and Crystal Structure of Novel Hollandite Compounds AxMgx/2Sn8 − x/2O16 (A = K, Rb, and Cs)

We have prepared novel hollandite compounds AxMgx/2Sn8−x/2O16 (A = K, Rb, and Cs) by solid state reaction, using A2CO3 (A = K, Rb, and Cs), Mg(NO3)2 ·6H2O and SnO2 in the molar ratio 1 : 1 : 3, at 1500°C for 5 hours in air. All compounds crystallize in the monoclinic space group C2/m. Their crystal structures and compositions were determined by the Rietveld analysis using X-ray powder diffraction data. K2MgSn7O16: a = 14.837(3) Å, b = 3.1667(1) Å, c = 10.490(2) Å, β = 134.919(8) Å, and Z = 1, RI = 7.32%. Rb2MgSn7O16: a = 14.890(4) Å, b = 3.1706(1) Å, c = 10.514(3) Å, β = 134.989(13) Å, and Z = 1, RI = 8.97%. Cs1.26Mg0.63Sn7.37O16: a = 15.015(3) Å, b = 3.1656(1) Å, c = 10.621(3) Å, β = 135.061(11) Å, and Z = 1, RI = 9.24%. Sn and Mg octahedra form the hollandite framework, and alkali ions are located in the hollandite tunnels. The Cs ion only partially occupies the tunnel, because the length of b-axis is shorter than Cs ion size. As a result, Cs hollandite only has the non-stoichiometric composition.