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Proton Potential and a Tunneling Model for KDP
Hiroyuki Mashiyama 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The parameters characterizing a Morse potential are estimated for a proton bonded with oxygen. The double-minimum potential for the hydrogen bonding in ferroelectric KH2PO4 is constructed by superposing two Morse potential functions. The energy levels are computed by solving onedimensional Schrodinger equation numerically. The susceptibility is calculated by using linear response theory and the mean-eld approximation. The two-level system is essential both for KDP and for DKDP, and the static susceptibility is represented by the Barrett equation. The theoretical phase diagram represents the essential feature of the pressure-temperature phase diagram for KDP and DKDP.
Ordering Process in Sodium Nitrite Observed by Using Neutron Diffractometry
Hiroyuki Mashiyama,Tatsuki Miyoshi,Takanao Asahi,Hironobu Kasano,Yukio Noda,Hiroyuki Kimura 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
From neutron diffraction data, the nuclear density of sodium nitrite is guessed directly by a maximum entropy method, and is compared with the results of usual least-squares calculations. The obtained nuclear density displays that the disordered NO_2 molecule becomes partially ordered in the ferroelectric phase just below the transition temperature. However, the density distribution cannot be explained by a two-Gaussian function, which suggests that the ordering is not a classical stochastic process but a quantum tunneling in a double minima local potential.
The Anti-Polar Structure of CH3NH3PbBr3
Hiroyuki Mashiyama,Y Kawamura,Y Kubota 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
The orthorhombic phase IV of MAPbBr3 was investigated by using synchrotron X-ray diffraction data from the powdered crystal measured by using a Debye-Scherrer camera. The diffraction pattern at 115 K was fitted by using a Rietveld method to refine the structural parameters. Some orthorhombic space groups, as well as monoclinic space groups, were tried to fit the data. The crystal symmetry was assigned as Pnma(Z = 4), a nonpolar space group with a = 7.976, b = 11.841 and c = 8.565 °A. The crystal structure of phase IV can be derived from cubic phase I, but not from tetragonal phase II. The polar MA ions are located in an anti-parallel way to cancel the polarization. The successive transitions are discussed from structural viewpoints.
Heat capacity, X-ray scattering and neutron scattering studies in Rb2SeO4
Hirotake Shigematsu,Hiroyuki Mashiyama,Hitoshi Kawaji,Takeo Tojo,Tooru Atake,Yukikuni Akishige 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The structural phase transition and behavior of the 2 3 phonon branch of Rb2SeO4 have been investigated with the use of heat capacity measurement and X-ray and neutron scattering technique. No phase transition was detected down to 2 K, both in thermal analysis and in neutron elastic scattering. However, neutron inelastic scattering showed a slight softening of the phonon excitation frequency below 100 K. Two typical trst-order-type anomalies due to the phase I - phase II transition and melting were observed at 821 K and 1233 K, respectively. The entropy change for the phase I - phase II transition was determined as 12.46 Jmol1K1.