New Polaronic-Type Excitons in Ferroelectric Oxides: INDO-Calculations and Experimental Manifestation

2001 ◽  
Vol 677 ◽  
Author(s):  
Valentin S. Vikhnin ◽  
Roberts I. Eglitis ◽  
Eugene A. Kotomin ◽  
Siegmar Kapphan ◽  
Gunnar Borstel
Keyword(s):  
Charge Transfer ◽  
Theoretical Knowledge ◽  
Strongly Correlated ◽  
Hartree Fock ◽  
Indo Calculations ◽  
Photoluminescence Studies ◽  
Ferroelectric Oxides ◽  
New Phase

ABSTRACTThe current experimental and theoretical knowledge of new polaronic-type excitons in ferroelectric oxides – charge transfer vibronic excitons (CTVE) – is discussed. It is shown that Hartree-Fock-type INDO calculations as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE-concept. Single CTVE as well as a new phase of strongly correlated CTVEs are analysed.

Theoretical Prediction and Experimental Confirmation of Charge Transfer Vibronic Excitons and Their Phase in ABO3 Perovskite Crystals

2002 ◽  
Vol 718 ◽  
Author(s):  
R. I. Eglitis ◽  
V. S. Vikhnin ◽  
E. A. Kotomin ◽  
S. E. Kapphan ◽  
G. Borstel
Keyword(s):  
Charge Transfer ◽  
Strongly Correlated ◽  
Hartree Fock ◽  
Abo3 Perovskite ◽  
Ionic Solids ◽  
Indo Calculations ◽  
Photoluminescence Studies ◽  
Ferroelectric Oxides ◽  
Neglect Of Differential Overlap ◽  
Vibronic Effect

AbstractThe current theoretical and experimental knowledge of new polaronic-type excitons in ferroelectric oxides - charge transfer vibronic excitons (CTVE) is discussed. It is shown that quantum chemical Hartree-Fock-type calculations using a semiempirical Intermediate Neglect of Differential Overlap (INDO) method (modified for ionic/partly ionic solids) as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE existence. Our INDO calculations for KTaO3 and KNbO3 have demonstrated that the triplet exciton is a triad centre containing one active O atom and two Ta atoms sitting on the opposite sites from this O atom. The total energy of a system is lowered by the combination of Coulomb attraction between electron and hole and the vibronic effect in this charge transfer vibronic exciton. It is shown by means of our INDO calculations that polaronic-type CTVE in ferroelectric oxides could lead to the formation of a new crystalline phase. The ground state energy of this phase consisting of strongly correlated CTVEs lies within an optical gap of a pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as by the ferroelectric ordering.

A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons

2001 ◽  
Vol 56 (5) ◽  
pp. 702-708 ◽  
Author(s):  
V. S Vikhnin ◽  
R. I Eglitis ◽  
S. E Kapphan ◽  
E. A Kotomin ◽  
G Borstel
Keyword(s):  
Charge Transfer ◽  
Ferroelectric Oxides ◽  
New Phase

Polarons and charge-transfer vibronic excitons in ferroelectric oxides: EPR and photoluminescence studies of Pb x Nb y O z ceramics

2005 ◽  
Vol 28 (1-2) ◽  
pp. 137-145 ◽  
Author(s):  
V. S. Vikhnin ◽  
R. I. Zakharchenya ◽  
H. R. Asatryan ◽  
A. B. Kutsenko ◽  
S. E. Kapphan
Keyword(s):  
Charge Transfer ◽  
Photoluminescence Studies ◽  
Ferroelectric Oxides

Study of charge transfer in FeTi

1983 ◽  
Vol 41 ◽  
pp. 296-297
Author(s):  
J. Taft∅
Keyword(s):  
Charge Transfer ◽  
Charge Distribution ◽  
Electron Scattering ◽  
Periodic System ◽  
Electron Distribution ◽  
Scattering Amplitude ◽  
Transition Elements ◽  
Hartree Fock ◽  
Cscl Structure ◽  
The Right

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.

Charge Transfer Vibronic Excitons, Bi-Polarons, and Iron Group Impurities in Ferroelectric Oxides: PbxNbyOz—Ceramics

2004 ◽  
Vol 307 (1) ◽  
pp. 67-76 ◽  
Author(s):  
V. S. VIKHNIN ◽  
R. I. ZAKHARCHENYA ◽  
H. R. ASATRYAN ◽  
A. B. KUTSENKO ◽  
S. E. KAPPHAN ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Iron Group ◽  
Ferroelectric Oxides

A strain-induced new phase diagram and unusually high Curie temperature in manganites

2017 ◽  
Vol 5 (31) ◽  
pp. 7813-7819 ◽  
Author(s):  
Yunfang Kou ◽  
Tian Miao ◽  
Hui Wang ◽  
Lin Xie ◽  
Yanmei Wang ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Critical Temperature ◽  
Curie Temperature ◽  
Functional Materials ◽  
Strongly Correlated Systems ◽  
High Curie Temperature ◽  
Strongly Correlated ◽  
Correlated Systems ◽  
Physical Phenomena ◽  
New Phase

Raising the critical temperature of functional materials is a major challenge for the exploitation of many exciting physical phenomena in strongly correlated systems.

Ferroelectric phase transition induced by charge transfer vibronic excitons in ferroelectric oxides

2004 ◽  
Vol 1 (11) ◽  
pp. 2820-2823 ◽  
Author(s):  
Valentin S. Vikhnin ◽  
Siegmar E. Kapphan ◽  
Rasa M. Pirc ◽  
Alexander S. Sigov
Keyword(s):  
Phase Transition ◽  
Charge Transfer ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Ferroelectric Oxides
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