Hironori Nakao

Temperature versus concentration phase diagram of Mg- and Si-doped CuGeO3

Abstract We studied the temperature versus concentration ( T – x ) phase diagram in Cu 1− x Mg x GeO 3 by susceptibility measurements, synchrotron X-ray diffraction and neutron diffraction and the first-order phase transition between dimerized-antiferromagnetic and uniform-antiferromagnetic phases reported by Masuda et al. [Phys. Rev. Lett. 80 (1998) 4566] was established. We found that the T – x phase diagram of Cu 1−x M x GeO 3 (M= Zn , Ni ) is similar to that of Cu 1− x Mg x GeO 3 , while that of CuGe 1− x Si x O 3 is qualitatively different.

Critical behavior of crystal lattice of NaV2O5

Abstract Critical behavior of crystal lattice was investigated by X-ray scattering for both stoichiometric NaV 2 O 5 and Na-deficient Na x V 2 O 5 ( x =0.99–0.96). Critical exponents were determined from superlattice reflections with a wave number vector Q =(1/2,1/2,1/4), specifying a lattice modulation formed below T C =35xa0K. The previously observed anomalous lattice strain below T C was found to be a secondary order parameter driven by a primary order parameter which is an atomic displacement with Q governing the low-temperature crystal structure. The temperature–concentration phase diagram was also determined and the transition temperature was found to decrease linearly with increasing deficiency x as d T C / d x=4.2 ( K /%).

Lattice dimerization and strain in inorganic spin-Peierls compound NaV2O5

Abstract X-ray and neutron scattering experiments of the new inorganic spin-Peierls compound show that below T sp = 36 K an anomalous volume expansion is proportional to the superlattice intensity associated with lattice dimerization. Also reported is the pressure effect on this compound which undergoes a phase transition around 13 GPa (room temperature).

Resonant x-ray scattering study on electronic hybridization in unconventional ordered phase of PrRu4P12

PrRu4P12, which undergoes a metal-insulator transition at TMI ~ 63 K, has been investigated by resonant x-ray scattering technique at the Pr L 3-edge, the P K-edge, and the Ru L 3-edge, in which element and orbital selective electronic states can be clarified. Resonating energy spectra at the 111 reflection were found at the Pr L 3-edge and P K-edge, while it was not observed at the Rh L 3-edge. This is the first observation of quite large resonant signal at the P K-edge. This result is considered as a direct evidence for the strong Pr 4f and P 3p hybridization effect on the unconventional ordered phase accompanied by the insulator state.

Er L3 -edge resonant elastic X-ray scattering study of orbital ordering in ErVO3

Introduction ErVO3 is one of an archetypal material of a t2g-orbital ordering system. Coupling of large orbital fluctuation and a lattice distortion causes two kinds of a characteristic order of dyz and dzx orbital. Below 195 K, these two orbitals are staggered three-dimensionally, namely the Gtype orbital order (G-OO). With more decreasing a temperature, they are aligned along c-axis below 60K corresponding to the phase transition from the G-OO to the C-OO [1]. Recently, pressure-experiment with a diamond-anvil-call has found an elevation of the transition temperature of the C-OO and decay of the GOO under a pressure. To explain the pressure effect, a covalency of the vanadium and surrounding ions (oxygen, A-site cation) is important as well as the band-width effect (Fig.1) [2].

Charge and orbital ordered states in Nd1−xSr1+xMnO4(x=0.67,0.75)

Abstract The charge and orbital ordered states in the single-layered manganite crystals, Nd 1−x Sr 1+x MnO 4 (x=0.67,0.75) , have been investigated. We have observed the superlattice spots with modulation wave vector, q=(δ,δ,0), δ= 1 8 , 1 4 [ ∼ 1 6 , 1 3 ] in x=0.75[0.67] by resonant and non-resonant X-ray scattering. These results show that not only the atomic displacement pattern but also the charge-orbital structure has the unit cell of 4 2 a× 2 a×c [3 2 a× 2 a×c] .