Activation Energy For Hopping Research Articles

Calculation on the Self-Trapped Hole in Solid Argon

Based on a simple model of a hole self-trapped in a VK-center-like configuration, the lattice relaxation, internal optical transition energies, and thermal activation energy for hopping of the self-trapped hole in solid argon are calculated. It is found that the molecular binding of Ar2+ is the predominating factor for the stability of this mode of self-trapping. The optical transition energies are found to be smaller than the corresponding energies in alkali halides. The most interesting result is about the activation energy for hopping which is smaller than 0.05 eV. It is suggested that the self-trapped hole in crystalline argon should be produced and studied at very low temperature, below about 20 °K.

Electrical Conductivity and Photoresponse in Tetracyanoquinodimethan

Abstract Dark and photoconductivity in tetracyanoquinodimethan have been measured in the temperature range of 170 °C to -35 °C. The majority carriers are electrons with hopping activation energy of 0.48 (± 0.05) eV. The band gap is estimated to be 2.05 eV and 2.31 eV from photoconductivity and transmission data respectively, with a temperature coefficient of 1.7 × 10−8 eV K−1.

Interpretation of M xV 2O 5-β and M xV 2− yT yO 5-β phases

The Wadsley Na 0.33V 2O 5-β structure is reexamined to demonstrate how the detailed atomic positions provide important information about the physical properties. After a review of the evidence for identifiable V 4+ ions, it is shown how, from the bond distances, to distinguish triple, double and single VO bonding with the d orbitals. From this analysis, it follows that the x electrons donated to the vanadium-oxygen array by M + ions are located in the d yz orbitals at positions V 1. Furthermore, consistency with the known properties of other vanadium oxides requires that the linear units V 2O 1V 2 form molecular d-state orbitals. It is noted that this changes the statistics entering the conventional formula for the small-polaron contribution to the Seebeck coefficient. Finally, the creation of a similar V 3O 7′V 3 d-state molecular unit is postulated for each M + ion that is introduced. It is argued that this analysis is supported by the following experimental results: (1) In the system Na x V 2− x Mo x O 5-β, the Mo atoms all go into V 2 positions if x ⩽ 0.33, but for x > 0.33 the V 2 positions contain ( 1 2 ) Mo + ( 1 2 ) V , presumably as Mo 6+O 1V 4+ units, and the excess ( x − 0.33) Mo atoms per formula unit occupy V 3 positions. (2) The Seebeck coefficient is accounted for without any adjustable parameter provided the linear units V 2O 1V 2 and one V 3O 7′V 3 per M + ion are counted as single available sites for small-polaron hopping. (3) Variation with x of the activation energy for electron hopping and of the magnetic susceptibility per small polaron extrapolate to collective-electron values for x > 0.67, which is consistent with a band of collective-electron orbitals of a V 3O 7′ array overlapping the energy of the d yz orbitals at V 1 sites for larger values of x. (4) The V 1V 1′ separation is too large for a small activation energy for conduction within the V 1 sublattice, but the large anisotropy for conductivity would also be consistent with conduction via the V 3O 7′ array. (5) The structure of Cu 0.60V 2O 5, which has the lower symmetry Cm, has atomic separations consistent with half of the V 1 sites of the Wadsley phase (symmetry C2 m ) donating electrons to half the Wadsley V 3O 7′ array. (6) The activation energy for conduction increases with y in the system Na 0.40V 2− y Mo y O 5-β. (7) The magnetic data is reviewed and, although not quantitatively accounted for because the magnetic properties of the excited states are not known, is shown to be consistent with a V 4+ ground state having its outer electron in the d yz orbital of a V 1 site.

The conduction processes in silicon nitride

The electrical conduction processes through silicon nitride are examined and discussed. Three processes were found to occur: Frenkel–Poole emission, field ionization, and trap hopping. The characteristic constant for the field ionization was found to be lower than expected (~5 × 106 V cm−1), and the thermal activation energy for the trap hopping was between 0.08 and 0.10 eV. The Frenkel–Poole effect indicated trap depths varying from 0.50 to 0.85 eV for various devices, and was more complicated than previously reported. All of the processes were bulk limited. Approximate values of m*/m and the mobility at 300 °K were found to be 0.20 and 0.13 cm2/V s respectively.

Investigation of quenched-in defects in Ge and Si by means of 64Cu

For the first time, 64Cu tracer measurements of ionic diffusion were performed for several copper-rich glass compositions in the CuIAs2Se3, CuISbI3As2Se3, CuIPbI2As2Se3, CuIPbI2SbI3As2Se3 and Cu2SeAs2Se3 systems. In accordance with previous a.c. impedance results and Wagner d.c. polarization measurements, it was found that pure Cu+ ion-conducting glasses (50CuI17PbI233As2Se3 and 50CuI20PbI210SbI320As2Se3) exhibit the highest copper tracer diffusion coefficients, DCu, and the lowest diffusion activation energies. The values of DCu at room temperature are higher by 4.5–5.5 orders of magnitude than those in an As2Se3 glass. The Haven ratio, HR, is found to be 0.52–0.61 (ternary glass) and 0.93–1.00 (quaternary glass). Short-range diffusional displacements of the iodide ions induced by the hopping Cu+ ions are also detected in the CuIPbI2SbI3As2Se3 glassy system using 129I-Mössbauer spectroscopy in the temperature range of 4.2 to 305 K. The activation energy of local hopping, Eh ≈ 0.31 eV, is very similar to that of bulk ionic conductivity (0.37 eV) and copper diffusion (≈ 0.33 eV). In contrast to CuI-based vitreous alloys, 50Cu2Se50As2Se3 glass exhibits DCu that are two to five orders of magnitude lower, and the copper ion transport number,tCu+, is between 10−3 and 10−4 in the temperature range 140–170 °C.