The Experts below are selected from a list of 1047 Experts worldwide ranked by ideXlab platform
Takashi Yanagisawa - One of the best experts on this subject based on the ideXlab platform.
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Madelung Energy of the Valence Skipping Compound BaBiO$_3$
Physical Review B, 2007Co-Authors: Izumi Hase, Takashi YanagisawaAbstract:Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the conventional electron-phonon mechanism. The reason for the missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO$_3$, and have shown for the first time that charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction Energy $U$ may be negative evaluating the local excitation Energy.
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Madelung Energy of the valence skipping compound babio _3
Physical Review B, 2007Co-Authors: Izumi Hase, Takashi YanagisawaAbstract:Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the conventional electron-phonon mechanism. The reason for the missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO$_3$, and have shown for the first time that charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction Energy $U$ may be negative evaluating the local excitation Energy.
Izumi Hase - One of the best experts on this subject based on the ideXlab platform.
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Madelung Energy of the Valence Skipping Compound BaBiO$_3$
Physical Review B, 2007Co-Authors: Izumi Hase, Takashi YanagisawaAbstract:Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the conventional electron-phonon mechanism. The reason for the missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO$_3$, and have shown for the first time that charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction Energy $U$ may be negative evaluating the local excitation Energy.
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Madelung Energy of the valence skipping compound babio _3
Physical Review B, 2007Co-Authors: Izumi Hase, Takashi YanagisawaAbstract:Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the conventional electron-phonon mechanism. The reason for the missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO$_3$, and have shown for the first time that charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction Energy $U$ may be negative evaluating the local excitation Energy.
Marc Fourmigué - One of the best experts on this subject based on the ideXlab platform.
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Pressure-Induced Neutral-Ionic Phase Transition in the Mixed-Stack 21 Charge-Transfer Complex (EDT-TTF-I-2)(2)TCNQF
Journal of Physical Chemistry C, 2020Co-Authors: Arkadiusz Frqckowiak, Di Liu, Roman Swietlik, Lucky Maulana, Martin Dressel, Olivier Jeannin, Marc FourmiguéAbstract:We explored the neutral-ionic phase transition in (EDT-TTF-I-2)(2)TCNQF by measuring the electrical conductivity as a function of temperature and hydrostatic pressure (up to 11.8 kbar). At about 4.3 kbar, the compound undergoes the transition to a quasi-ionic phase at the temperature about 100 K; the transition temperature increases as the pressure grows. We propose a pressure-temperature phase diagram, discussed in comparison to analogous data obtained for mixed-stack 11 charge-transfer complexes, which also undergo a neutral-ionic transition. We suggest that the transition smearing can be related with the fact that, in this 21 complex, not only the Madelung Energy but also the ionization potential of donors grows as the crystal lattice contracts upon decreasing temperature.
Hiroshi Katayama-yoshida - One of the best experts on this subject based on the ideXlab platform.
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Physics and control of valence states in ZnO by codoping method
Physica B-condensed Matter, 2001Co-Authors: Tetsuya Yamamoto, Hiroshi Katayama-yoshidaAbstract:We investigate unipolarity in ZnO based on ab initio electronic band structure calculations. We find that p-type doping using Li, N or As species causes an increase in Madelung Energy, n-type doping using B, Al, Ga, In or F species gives rise to a decrease in Madelung Energy. In order to solve the unipolarity, to fabricate p-type ZnO, we propose a codoping method using acceptors and reactive donors simultaneously. A codopant pair including Ga-reactive donors and N-acceptors is eminently suitable for use in the codoping. For Li-acceptors, F species is a good candidate for reactive donors. For As-acceptors, Ga species is a preferable codopant.
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Solution Using a Codoping Method to Unipolarity for the Fabrication of p-Type ZnO
Japanese Journal of Applied Physics, 1999Co-Authors: Tetsuya Yamamoto, Hiroshi Katayama-yoshidaAbstract:We have investigated the electronic structures of n- or p-type doped ZnO based on ab initio electronic band structure calculations. We find unipolarity in ZnO; n-type doping using Al, Ga or In species decreases the Madelung Energy while p-type doping using N species increases the Madelung Energy, in addition to causing substantial localization of the N states. Codoping using reactive codopants, Al, Ga or In, enhances the incorporation of N acceptors in p-type codoped ZnO. We find the delocalized states of N for p-type ZnO codoped with N and Al (Ga).
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Role of n -Type Codopants on Enhancing p -Type Dopants Incorporation in p -Type Codoped Znse
MRS Proceedings, 1998Co-Authors: Tetsuya Yamamoto, Hiroshi Katayama-yoshidaAbstract:We propose materials design for the fabrication of low-resistivity p -type ZnSe crystals using a new doping method which involves simultaneous codoping of both n - and p -type dopants, based on the ab initio electronic band structure calculations. We have clarified that while doping of acceptor dopants, Li zn and N se , leads to the destabilization of the ionic charge distributions in p -type ZnSe crystals, doping of donor dopants, In zn , Cl Se or ISe gives rise to n -type doped ZnSe with high donor concentration due to a large decrease in the Madelung Energy. The codoping of the n - and p -type dopants (the ratio of their concentrations is 1:2) enhances the incorporation of the acceptors in p -type ZnSe crystals due to a decrease in the Madelung Energy, resulting in the formation of the p-n-p complexes which occupy nearest-neighbor sites. It results in an increase in the net carrier densities and the hole mobility due to a change in the scattering mechanism from that caused by long-range Coulomb scatters to that by short-range dipole-like ones
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Control of valence states by a codoping method in CuInS2
Solar Energy Materials and Solar Cells, 1997Co-Authors: Tetsuya Yamamoto, Hiroshi Katayama-yoshidaAbstract:We deviate the valence and conduction band energies of stoichiometric CuInS2 crystals based on ab initio electronic band structure calculations using the augmented spherical wave (ASW) method and discuss that at low doping levels, the Madelung Energy is a good intrinsic parameter for stabilization of p- or n-type doped CuInS2 crystals. We find that P and Sb atoms are eminently suitable dopants substituted for S atoms for p-type doped CuInS2 crystals with lower resistivity from both the character of electronic states around EF and the Madelung Energy. A closer study of the nature of chemical bonds of CuInS2 crystals using first-principles band structure calculation method reveals that In with polyvalence codoping for p-type CuInS2 doped with P results in a decrease of the Madelung Energy compared with CuInS2: P, to be an effective method for stabilizing of its ionic charge distributions.
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Materials Design of the Codoping for the Fabrication of Low-Resistivity p-Type ZnSe and GaN by ab-initio Electronic Structure Calculation
physica status solidi (b), 1997Co-Authors: Hiroshi Katayama-yoshida, T. YamamotoAbstract:We propose an effective doping method, the “codoping (doping with n- and p-type dopants at the same time) method”, for the fabrication of low-resistivity p-type ZnSe and GaN with wide-band-gap based upon ab-initio electronic band structure calculations. p-type doping eminently leads to an increase in the electrostatic Energy, called the Madelung Energy, which shifts the Se 4p levels for p-type doped ZnSe and the N 2p levels for p-type doped GaN materials towards higher Energy regions. This leads to a destabilization of ionic charge distributions in p-type ZnSe and p-type GaN crystals, resulting in the self-compensation of anion intrinsic defects. For ZnSe crystals, we propose the codoping of n-type In donors at Zn sites and p-type N acceptors at Se sites based on the calculation. In addition, we propose the codoping of n-type Si-donors at Ga sites (n-type O donors at N sites) and p-type Be- or Mg acceptors at Ga sites. The codoping decreases the Madelung Energy and leads to an increase in the net acceptor carrier density.
Hee Young Lee - One of the best experts on this subject based on the ideXlab platform.
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Phase Stability of Tungsten-Bronze-Structured KLN Ceramics: Effect of Excess Nb_2O_5
Journal of Electroceramics, 2004Co-Authors: Chul-young Jang, Joon-hyung Lee, Jeong-joo Kim, Sang-hee Cho, Hee Young LeeAbstract:The effect of excess Nb_2O_5 on the phase stability of tungsten-bronze-structured K_3Li_2Nb_5O_15 (KLN) ceramics was studied. Stoichiometric KLN ceramics are not obtained as a single phase and second phases of KNbO_3 and Li_3NbO_4 were observed. Additionally, stoichiometric KLN is difficult to sinter. In Nb-rich compositions, the second phase disappeared and a single KLN phase was obtained. This phase development behavior, that is, the phase stability of the KLN, was analyzed from the viewpoint of the electrostatic potentials of ions. The calculated Madelung Energy of the completely filled stoichiometric KLN was unstable, while Nb-rich compositions showed much reduced Madelung Energy, indicating that the ions were stabilized electrostatically. Enhanced sinterability in Nb-rich compositions is also discussed.
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Phase stability of tungsten-bronze-structured KLN ceramics: Effect of excess Nb2O5
Journal of Electroceramics, 2004Co-Authors: Chul-young Jang, Joon-hyung Lee, Jeong-joo Kim, Sang-hee Cho, Hee Young LeeAbstract:The effect of excess Nb2O5 on the phase stability of tungsten-bronze-structured K3Li2Nb5O15 (KLN) ceramics was studied. Stoichiometric KLN ceramics are not obtained as a single phase and second phases of KNbO3 and Li3NbO4 were observed. Additionally, stoichiometric KLN is difficult to sinter. In Nb-rich compositions, the second phase disappeared and a single KLN phase was obtained. This phase development behavior, that is, the phase stability of the KLN, was analyzed from the viewpoint of the electrostatic potentials of ions. The calculated Madelung Energy of the completely filled stoichiometric KLN was unstable, while Nb-rich compositions showed much reduced Madelung Energy, indicating that the ions were stabilized electrostatically. Enhanced sinterability in Nb-rich compositions is also discussed.
