G. Spano

Thermoluminescence experiments to study lattice defects in aluminosilicates

SummaryThe thermoluminescent emissions of β-eucryptite and β-spodumene have been recordedvs. temperature and wavelength. Arguments are advanced which allow the observed emission to be ascribed to point defects originated by the exchange of Si+4 and Al+3 ions in (Si, Al)O4 tetrahedra.

A Debye model for point defects in aluminosilicate crystals

SummaryIn aluminosilicate lattices, exchanges between silicon and aluminum ions are expected to originate charged point defects of opposite signs. Thermodynamic arguments, based on a model analogous to the Debye electrolyte model, allow evaluation of the equilibrium density of defects as a function of temperature. The electric field of point defects is found to be screened by charge distribution even at distances small enough to affect the ground-state energy of electrons trapped by the defect positive charges. Calculations show that large fluctuations of trapped electron energy are expected. These results agree with data from thermoluminescence experiments on different aluminosilicates, which showed broad distributions of electron traps.

Investigation on CaF2 lattice defects by thermoluminescence experiments

SummaryThe X-ray excited thermoluminescent emission of calcium fluoride has been recorded simultaneouslyvs. temperature and wavelength. Samples of different origin, but of good chemical purity, were examined, both untreated and treated at 1100 and 1300°C. A variety of thermoluminescent patterns has been obtained, but after treatment at 1300°C all samples show practically the same pattern. The features of the emission observed are readily interpreted on the ground of kinetic models for the thermoluminescent process. Some information is obtained about the presence and nature of lattice defects originating electron traps and luminescent centres.

Mössbauer spectroscopy of tektites

SummaryDifferent tektite samples have been investigated by57Fe room temperature Mössbauer spectroscopy. The data indicate iron degrees of oxidation larger than those previously determined by wet chemical analysis.

Thermodynamics of ion exchange defects in aluminosilicates

SummaryThe Debye-Huckel model for electrolytes is utilized to evaluate the density of defects originated by the exchange of Al and Si ions in aluminosilicate lattices.

A study of KCL lattice defects by thermoluminescence experiments

SummaryThe thermoluminescent emission of X-irradiated potassium chloride is recorded simultaneouslyvs. temperature and wavelength. Samples of different origin and prepared through different processes, including thermal treatments, are examined. Most records show essentially two glow peaks, the wavelength of the one at higher temperature being slightly shifted toward the red. On the whole, experimental results suggest that luminescent centres are originated by potassium ion vacancies lying at a variable distance from interstitial potassium ions. The observed red shift is ascribed to the Coulomb energy of the pairs of these point defects of opposite charges.

A study of lattice defects in solids belonging to Al2O3−B2O3 and Al2O3−SiO2 systems by thermoluminescence experiments

SummarySpectrally resolved thermoluminescent emission has been investigated in solids belonging to Al2O3−B2O3 and Al2O3−SiO2 systems. These solids, which are characterized by a structure like that of alumino-silicate mullite, contain a high density of oxygen and aluminum or boron lacunae. This fact favours the occurrence of both-sign interstitial ions acting as carrier traps. The results show a close similarity with those obtained when studying, with the same experimental method, the thermoluminescent emission of alumina. The overall analysis of data allows for reliable conclusions on the nature of crystal defects in these materials.

Investigation of alumina lattice defects by means of thermoluminescence experiments

SummarySamples of α-alumina prepared at low temperature by means of a special procedure are investigated by recording their thermoluminescent emissionvs. temperature and wavelength. Taking into account the effect of thermal treatments, evidence is obtained for the presence of a distribution of electron traps of different depths. Arguments are advanced for characterizing the nature of the lattice defects originating these traps.

Is positron annihilation a suitable tool for investigating high-T c superconductors?

SummaryThe effectiveness of the positron annihilation method for gaining information on electron momentum distribution in high-Tc superconductors is discussed critically. The few available experimental results are considered. The possibility of making substantial improvements in the experimental technique is examined in some detail.

Investigation of cordierite lattice defects by thermoluminescence experiments

SummaryThe thermoluminescence of α- and μ-cordierite samples has been recordedvs. temperature and wavelength. Arguments ascribing the observed emission to the easy ion exchanges characterizing cordierite lattices are advanced.