J. D. Comins

Behavior of elastic constants, refractive index, and lattice parameter of cubic zirconia at high temperatures

Acoustic mode frequency, lattice parameter, and refractive index measurements have been carried out on single crystals of cubic stabilized zirconia, ZrO2(xY2O3), in the temperature range 300 to 1450 K, using Brillouin scattering, x‐ray diffraction, and interferometric methods, respectively. Elastic constants Cij and associated quantities such as the bulk modulus B=(C11+2C12)/3, the anisotropy ratio A=2C44/(C11−C12), and the Cauchy relation failure Δ=(C12−C44) have been determined from these measurements. The results show a linear reduction in C11 , C12 , and C44 until a characteristic transition temperature Tc, which depends on the dopant concentration x. The linear decrease is understood in terms of normal thermal expansion. Above Tc (1300 K for x=9.4 mol % and 1050 K for x=24 mol %) there are elastic anomalies; significant reductions in C11, (C11‐C12)/2 and C44 occur, with an increase in C12 . These effects are considered to result from thermally generated disorder. Detailed examination of the temperatu...

High‐temperature elastic constants of yttrium aluminum garnet

Elastic constants of yttrium aluminum garnet have been measured in the temperature range 300–1450 K using a combination of Brillouin scattering and refractive index measurements. Associated quantities such as the bulk modulus, anisotropy ratio, and thermo‐optic coefficient have been determined.

Brillouin scattering from acoustic excitations in TiN films on high speed steel—A stiffening system

Brillouin scattering measurements are presented of surface acoustic waves in TiN films of various thicknesses on high speed steel. Because of its relatively high elastic moduli as compared with those of steel, TiN has a stiffening effect on the surface, causing the surface acoustic wave (SAW) to increase in velocity, merge into the bulk wave continuum, and become a pseudo-SAW. In the limit of large film thickness this pseudo-SAW evolves into the Rayleigh wave for TiN. A Green’s function method, invoking the surface ripple mechanism for the inelastic scattering of light, is used to calculate the Brillouin spectrum for scattering from these surface acoustic modes, and reveals details of the acoustic excitations of stiffening thin films not previously appreciated. A comparison between the measured and calculated dispersion relation for TiN thicknesses ranging from 20 to 4180 nm reveals that the elastic moduli of the thicker films are close to those of bulk TiN, but the effective elastic moduli of the thinner...

Defect clusters and thermoluminescence in LiF crystals

The thermoluminescence of pure and doped LiF crystals has been measured following irradiation at ambient temperature with gamma and x rays. Factors investigated include the effects of dopants (Mg, Mg/Ti, and Fe) and of dose. Results are compared with optical absorption and photoluminescence measurements made previously on the same crystals. The role of F, F3+, Z2, and colloids in the emission process is discussed. Some new effects are reported including step-like features in the glow curves at large doses. These are explained in terms of the clustering of interstitial defects formed during radiolysis.

Photoluminescence and the thermal stability of color centers in γ-irradiated LiF and LiF(Mg)

Pure and magnesium doped (2000 ppm) LiF crystals have been irradiated with γ rays from 241Am and 60Co sources and the thermal stability of the resulting defects has been studied using photoluminescence (PL) and optical absorption (OA). The composite nature of the M band at 440 nm is highlighted by PL data which reveal emission attributed to F3+ defects otherwise hidden in OA measurements. The following bands appear in excitation spectra; Z3 (222 nm), Z2 (285 nm), R1 (329 nm), R2 (375 nm), F3+ (440 nm), and F2 (440 nm). Notable differences are observed between pure and doped samples during thermal annealing relating to the F2 and F3+ bands in particular. Results support the idea of Z centers as being F and F− centers trapped at impurity ions in the crystal.

The production of defects and colloids in lithium fluoride crystals by implantation with rare gas ions

Optical absorption spectra in the range 2 eV to 12 eV are presented for lithium fluoride crystals implanted with rare gas ions argon and neon of energy 100 keV. F- and M-centres are produced by bot...

Measurements of elastic constants in super-ionic Ba1-xLaxF2+x

Measurements of Brillouin frequency shifts as a function of temperature have been performed on BaF2 and Ba1-xLaxF2+x (x=0.393). In BaF2 the associated elastic constant C11 shows a pronounced decrease at Tc which continues up to the highest temperature measured, whereas C44 is unaffected. In Ba1-xLaxF2+x both C11 and C44 show decreases at a lower value of Tc, these decreases tending to saturate at higher temperatures. The results are examined in the light of models of highly defective fluorites.

Halogen defect aggregation in KI irradiated between 195 K and 295 K

Abstract Annealing experiments, in conjunction with optical absorption and Raman scattering measurements, have been undertaken previously on KI, X- or γ-irradiated at 195 K and 295 K, in order to study the mechanism of halogen interstitial aggregation. Irradiation at 195 K resulted in the prominent formation of I − 3 clusters whereas at 295 K large molecular aggregates ( I 2 ) n were preferentially formed. The present studies at the intermediate temperatures of irradiation, 233 K and 273 K have provided important information clarifying the progressive nature of halogen cluster development. At these temperatures I − 3 , I − n and ( I 2 ) n clusters are formed. The ( I 2 ) n clusters become increasingly dominant as the temperature of irradiation is raised. The role of the I n clusters is examined.

Study of defect annealing in γ-irradiated KI by Raman scattering and optical absorption

The annealing behaviour of defects produced in KI by gamma -irradiation at 198K has been studied by optical absorption and Raman scattering techniques. During isochronal annealing, the major optical absorption features, the F band and the double-peaked V band decay at 338K in unison with the 113 cm-1 Raman peak attributed to I3- interstitial halogen complexes. This identifies the I3- complexes as the major centres complementary to the F centres and responsible for the V band. Isothermal and isochronal annealing studies indicate second-order kinetics for the 338K stage and an activation energy of 1.4 eV. The other substantial Raman feature observed at 173 cm-1 and attributed to In- (n=5 . . .) halogen complexes is shown to decay at 378K, but is not obviously correlated with any optical absorption feature. It is suggested that these defects are associated with interstitial dislocation loops on their precursors.

Study of defect formation in irradiated KI and KI(Pb) by raman scattering and optical absorption techniques

Abstract Studies of the growth of halogen molecular complexes induced in KI and KI(Pb) have been made by Raman scattering and optical absorption techniques. Their behaviour is consistent with the ideas of halogen cluster development resulting from the sequential trapping of halogen interstitials. Comparison of the results with recently published studies of KI and KI(Ca) shows that the defects responsible for the Raman scattering (I3- and higher order interstitial complexes) have the same basic nature independent of the presence of nearby impurities. Evidence that lead impurities stabilize halogen interstitials is presented.