K. A. K. Lott

Electron spin resonance in phosphate glasses containing mixed transition metal ions

Phosphate glasses containing mixed Cu2+/Ni2+ and Cu2+/Co2+ oxides have been examined. A pronounced decrease in the optical absorption at 830 nm due to the Cu2+ ions is observed as the CuO in the glasses is gradually replaced by NiO or CoO and the decrease is accompanied by a pronounced decrease in the strength of the electron spin resonance (ESR) signal at 9.52 GHz. By combining the ESR and optical absorption data it is concluded that the decrease in concentration of Cu2+ ions in phosphate glasses may be due to an oxidation-reduction mechanism between two valency states of the two different transition metals, of the form Cu2++Ni+→Cu++Ni2+ and Cu2++Co+→Cu++Co2+.

ESR studies of thin amorphous films of MoO3-effects of substrate temperature, film thickness and annealing procedures

Electron spin resonance spectra of thin films of amorphous MoO3 are presented. An increase in spin density associated with increased Mo(V) concentration is found to occur with increased substrate deposition temperature. Plots of spin density against film thickness show a linear relationship, and reveal a significant residual spin density when extrapolated to zero thickness. Resonance signals are observed atg = 1.92 andg = 2.0 which are attributed to Mo(V) and Mo(III), respectively; that atg = 1.92 vanishes on annealingin vacuo at 250° C. Colour centres observed at higher substrate temperatures are probably due to the presence of Mo(III).

Electron spin resonance study in P2O5-MoO3 and P2O5-MoO3-CaO glasses

ESR spectra of the glass systems P2O5-MoO3 and P2O5-MoO3-CaO are presented. The electron spin resonance results showed a strongly exchange-narrowed interaction with the [Mo5+]/[Mo6+] ratio and line shapes independent of temperature over the range 77 to 300 K. This result supports the concept of temperature-dependent mobility of the carriers and an unchanged paramagnetic site over this temperature range. The more important difference between the spectra of the binary and ternary glasses is that in the former with an increase in MoO3 content the concentration of Mo5+ ions decreases but in ternary glasses it is reversed, i.e. the ion concentration of Mo5+ increases with increase in MoO3 content.

A study of electron spin resonance in copper-phosphate glasses containing praseodymium

The e.s.r. spectra of glasses of compositions (P2O8)65(CuO)35−x(Pr6O11) and (P2O5)65(CuO)25-(CaO)10−x(Pr6O11)x, wherex varied from 0 to 5 mol %, were measured. From the results and the chemical analyses of the samples it is found that the reduced valency ratioC of the copper in the glasses investigated generally increases with increasing Pr6O11 content. In our samples it is believed that enhanced chemical reduction of the cupric (Cu2+) ion is a consequence of its interaction with a reduced ion of the added praseodymium oxide.

An electron spin resonance study of copper phosphate glasses containing some rare earth oxides

The electron spin resonance spectra of phosphate glasses containing mixed Cu2+-Er3+ and Cu2+-Lu3+ oxides have been examined. A reduction in the copper (II) signal intensity in the glasses as the proportion of rare earth oxide is raised corresponds to an increase in the reduced valency ratio C in the glasses. Differences between the behaviour of glasses containing erbium and those containing lutetium are observed and probably arise from magnetic coupling between copper (II) and erbium (III).

A study of electron spin resonance phenomena in TeO2-CuO-CuCl2 glasses

We present the results of ESR powder spectra taken on unannealed glass samples having the composition 65TeO 2 -(35-x)CuO-xCuCl 2 with x varying from 1 to 5 in mol%. ESR studies were carried out tube at room temperature and at X-band frequency

A relaxation trend in the electron spin resonance phenomena in copper tellurite glasses containing NiO, CoO and Lu2O3

Copper tellurite glasses containing NiO, CoO and Lu2O3 were prepared by the melt-quenching technique. The composition used was 65TeO2-(35-x)CuO-xTMO (mol%), where TMO indicates NiO, CoO, Lu2O3, and for NiO- and CoO-doped glasses,x has the values 0, 0.5, 1 to 4, and for Lu2O3 doped glasses x=0 to 4. Electron spin resonance (ESR) spectra of all glasses were recorded at room temperature. The results on glasses doped with NiO, CoO and Lu2O3 are discussed in terms of oxidation-reduction, cross-relaxation and interelectronic repulsion processes, respectively. Cobalt oxide is found to be more effective in relaxing the ESR spectrum than nickel and lutetium oxides when substituted in copper tellurite glasses.

The effect of composition, substrate temperature and annealing on the paramagnetic centres in SiO x /SnO co-evaporated thin films

The effects of composition and substrate temperature during evaporation and annealing, on the electron spin resonance spectra of co-evaporated SiOx/SnO (300 nm) thin films have been investigated. The spin density is observed to decrease with increasing SnO content. This effect is attributed to the saturation of some of the paramagnetic defects such as dangling bonds and other structural defects like E′1 centres. The decrease in spin density in the composite thin films of SiOx/SnO of constant thickness and composition with annealing and with increase in the substrate temperature during evaporation, is related to the conversion of some of the paramagnetic E′1 centres to E″1 (probable non-paramagnetic precursor of E′1) centres as well as to the saturation of some of the dangling bonds.

Electron spin resonance and electrical properties of co-evaporated SiO/SnO2 thin films

Electron spin resonance (ESR) measurements are reported for various compositions of SiO/SnO2 thin films and indicate a decrease in the value of spin density for increasing SnO2 content in the SiO. Annealing of the device further reduces the value of the spin density. The electrical activation energy and resistivity have been found to increase after annealing of the device and the results are compared with the optical and ESR measurements.

A study of electron spin resonance of copper phosphate glasses containing tellurium oxide

Electron paramagnetic resonance in glasses of compositions (P2O5)100−x-(CuO)x and (P2O5)50-(TeO2)50−x-(CuO)x where x varied from 20 to 40 mol% has been investigated. The distribution of the copper between the two main valency states is determined from measurements of e.s.r. arising from the Cu2+ centres. The study of e.s.r. enables the distribution of copper in the glasses between the different valency states to be determined and thus indirectly provides evidence for hopping conduction in the glasses. From the results of e.s.r. and the chemical analysis of the samples it is found that the reduced valency ratioC, i.e. the ratio of the concentration of Cu+ ions to that of total copper in the glass, increases with increasing CuO content.