The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

Electron spin relaxation of the PO3 2- radical in ferroelectric betaine phosphite and in the proton glass betaine phosphate/betaine phosphite

Measurements of the electron spin-lattice relaxation time T1 and the phase memory time TM of the PO3 2- radical in γ-irradiated betaine phosphite and betaine phosphate/betaine phosphite are presented. The temperature dependence of T1 indicates the interaction of the electron spin with two groups of optical branches via Raman processes in both crystals. An additional relaxation path due to the interaction with two-level local tunneling states has been observed in the mixed crystal confirming glassy behaviour. The TM temperature dependence reflects thermally activated local motional effects of the PO3 group in both crystals. © 1994

Evidence of the Jahn-Teller splitting of C60- in C60- tetraphenylphosphoniumchloride from an electron-spin-relaxation study

Pulsed EPR measurements of the transverse and longitudinal relaxation times of the C60 - anion radical in crystalline C60-tetraphenylphosphoniumchloride were done at temperatures from 4 to 40 K. Above 40 K to room temperature the longitudinal relaxation time was taken from the cw-EPR linewidth. The low-temperature data are explained in terms of local magnetic fluctuations, slow C60- motion, and localized two-level states related with the local disorder. The relaxation data at higher temperatures reveal experimental evidence for the Jahn-Teller distortion of the C60 - anion radical and allow to determine the Jahn-Teller splitting between the a2u electronic ground state and the excited e1u state of the unpaired electron. © 1995 The American Physical Society

A Q-Band Pulsed ENDOR Spectrometer for the Study of Transition Metal Ion Complexes in Solids

We describe the design of a pulsed electron nuclear double resonance (ENDOR) spectrometer operating at Q-band frequencies (35 GHz) for studies of transition metal ion complexes in the temperature range between 4.2 and 297 K. Specific features of the spectrometer are a microwave IMPATT generator, a homebuilt cavity, and a commercial Bruker magnet. Standard Davies and Mims ENDOR sequences have been implemented. The performance of the spectrometer is demonstrated for a broad radio frequency range by 1H, 14N, 31P, 133Cs, and 207Pb pulsed ENDOR experiments of Cu 2+, Cr 5+, and V 4+ transition metal ion complexes in both single crystals and disordered materials

EPR, ESE and pulsed ENDOR study of nitrogen related centers in 4H-SiC wafers grown by different technologies

D-band electron paramagnetic resonance (EPR) measurements as well as X and Q-band field-swept Electron Spin Echo (ESE) and pulsed Electron Nuclear Double Resonance (ENDOR) studies were performed on a series of n-type 4H-SiC wafers grown by different techniques including sublimation sandwich method (SSM), physical vapor transport (PVT) and modified Lely method. Depending on the C/Si ratio and the growth temperature the n-type 4H-SiC wafers revealed, besides a triplet due to nitrogen residing on the cubic site (Nc), two nitrogen (N) related EPR spectra with g||=2.0055, g⊥=2.0010 and g||=2.0063, g⊥=2.0005 with different intensities. In the samples with low C/Si ratio the EPR spectrum with g||=2.0055, g⊥=2.0010 consists of a triplet with low intensity which is tentatively explained as a N-related complex, while in the samples with high C/Si ratio the triplet is transformed into one structureless line of high intensity, which is explained as being due to an exchange interaction between N donors. In the samples grown at low temperature with enhanced carbon concentration the EPR line with g||=2.0063, g⊥=2.0005 and a small hyperfine (hf) interaction dominates the EPR spectrum. It is attributed to N on the hexagonal lattice site. The interpretation of the EPR data is supported by activation energies and donor concentrations obtained from Hall effect measurements for three donor levels in this series of 4H-SiC samples

The ASSET Architecture - Integrating Media Applications and Products through a Unified API

International audienceApplications and products currently available for the broadcasting market are vertically integrated or proprietary. They are based on components requiring specific and costly development to interoperate and do rely typically on a single manufacturer or system integrator. Hence they are not fully compliant with broadcasters' requirements. ASSET is a European funded project whose main goal is to overcome the limitations of custom specific implementations of a digital system for TV content creation. These limitations are generally due to the misfit of interfaces between software layers, proprietary APIs of equipment from different vendors and the lack of a generalised middleware for multimedia content management with openly defined interfaces. Besides presenting the ASSET proposed architecture and concepts, this paper describes the prototype under development to test and demonstrate the project proposals

The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

Electron spin relaxation of the PO3 2- radical in ferroelectric betaine phosphite and in the proton glass betaine phosphate/betaine phosphite

Measurements of the electron spin-lattice relaxation time T1 and the phase memory time TM of the PO3 2- radical in γ-irradiated betaine phosphite and betaine phosphate/betaine phosphite are presented. The temperature dependence of T1 indicates the interaction of the electron spin with two groups of optical branches via Raman processes in both crystals. An additional relaxation path due to the interaction with two-level local tunneling states has been observed in the mixed crystal confirming glassy behaviour. The TM temperature dependence reflects thermally activated local motional effects of the PO3 group in both crystals. © 1994