H. W. den Hartog

Infrared spectroscopy of network and cation dynamics in binary and mixed alkali borate glasses

Infrared reflectance spectra of twenty different glasses of the type (B2O3)1-x-y(Li2O)x(Cs2O)y have been measured in the frequency range of 10–5000 cm−1. From these spectra, infrared absorbance and dielectric spectra have been calculated using the Kramers-Kronig inversion technique. The mid-infrared parts of the spectra are discussed in connection with BO network vibrational modes. The far-infrared parts of the spectra yield cation vibrational modes, which distinctly depend on the glass composition. The occurrence of two absorbtion bands for each cation species is associated with single and double occupation of network sites. It appears that the Li+ ionic vibrations are a sensitive function of the local network structure, but that the Cs+ ionic vibrations depend only on the total charge provided by a larger part of the surrounding glass network. In the binary lithium-containing glasses, a dielectric relaxation at ≈ 60 cm−1 arises. This relaxation is assigned to an ‘unsuccessful hop’ mode. The far-infrared dielectric results can be connected smoothly to dielectric spectra in the GHz region.

The structure and conductivity of binary and ternary glasses (b2o3)1-x-y(Li2O)x(Li2Cl2)y

The ionic conductivity of the glasses of the type (B2O3)1-x(Li2O)x and (B2O3)1-x-y(Li2O)x (Li2Cl2)y, has been investigated. In order to understand the superionic properties of these glasses, several experimental techniques have been employed. We present experimental results of density measurements, differential scanning calorimetry, ionic thermocurrents (ITC) and dielectric loss measurements in the frequency range 100–30000 Hz. It appears that the activation energy of the ionic conductivity decreases with increasing Li2O content. The addition of LiCl probably does not influence the glass structure, which will be discussed in some detail. The presence of LiCl in lithium borate glasses, however, causes a drastic increase of the ionic conductivity, which cannot be accounted for by the increased number of charge carriers only. Also the activation energy associated with the conductivity of Li+ ions is reduced by the presence of Cl− ions.

Structure and dynamics of alkali borate glasses : a molecular dynamics study

Structural and dynamical properties of lithium, cesium and mixed alkali (i.e., lithium and cesium) borate glasses have been studied by the molecular dynamics method. The calculations yield glass structures consisting of planar BO3 triangles and BO4 tetrahedrons with no sixfold ring structures at all. Alkali ions show a strong preference to reside in the vicinity of nan-bridging oxygen atoms, a tendency which is stronger for lithium ions than for cesium ions. The experimental Raman peaks at 805 and 770 cm(-1) are reproduced by symmetric breathing modes of BO3 and BO4 units, respectively. Simulated infrared absorption spectra reproduce the experimental spectra quite well. It appears that the velocities of different cesium ions show much more correlation than those of the lithium ions and that the frequency spectra of Li+ and Cs+ ions are in good agreement with far-infrared measurements.

Raman spectroscopy study of (B2O3)1−x−y(Li2O)x(Li2Cl2)y and (B2O3)1−x−y(Li2O)x(Cs2O)y

Raman spectra of glasses of the types (B 2 O 3 ) 1− x − y (Li 2 O) x (Li 2 Cl 2 ) y and (B 2 O 3 ) 1− x − y (Li 2 O) x (Cs 2 O) y are presented. The Raman studies have been carried out between 20 °C and 500 °C. The most important features of the spectra, the sharp and intense bands at 770 and 805 cm −1 , are attributed to symmetrical, six-coordinated rings in the boron-oxygen network structure. The intensity ratios of these bands ( I 7770 /I 805 ) provide useful information of the glass structure. These results are compared with the glass transition temperature data of these glasses. It is concluded that the glass network structure of lithium borate glass remains unchanged if LiCl is added. The Cl − ions do not take part in the boron-oxygen network. Just as the Li + ions, they will be incorporated in interstitial vacancies of the network. The replacement of Li + ions by Cs + ions in lithium borate glass leads to an enhanced number of nonbridging oxygens (NBOs) in the glass network; in addition it leads to a preference to form borate rings with one BO 4 unit instead of borate rings with two BO 4 units.

NEW INSIGHTS INTO THE STRUCTURE OF B2O3 GLASS

Abstract The results of structural investigations of various types of B 2 O 3 glass with different thermal histories are presented. The density and the glass transition temperature T g depend on the cooling rate at which the glass is quenched. For quickly quenched glass (cooling rate 10 3 K/s) the density is 1.79 g/cm 3 and T g is 278°C whereas these values for slowly quenched glass (cooling rate 4 × 10 −3 K/s) are respectively 1.83 g/cm 3 and 298° C. X-ray diffraction and Molecular Dynamics simulations show that the structure of vitreous B 2 O 3 can be explained by a model of randomly connected BO 3 triangles. The slower the glass is quenched, the more the BOB angles of adjacent BO 3 units approach 120°. We have found no tendency of neighbouring BO 3 triangles to form equiplanar complexes if the cooling rate decreases and therefore we have found no evidence for the existence of boroxol rings. The combination of the results of density measurements and X-ray diffraction studies indicates that for the slowly quenched glass the oxygen tend to be out of the plane of adjacent BO 3 triangles. This results in a more densely packed glass structure for slowly quenched B 2 O 3 glass.

A molecular dynamics study of B2O3 glass using different interaction potentials

Molecular dynamics calculations of B 2 O 3 glass were carried out, using seven different interaction potential schemes. Two-body Born-Mayer-Huggins potentials and in some samples also three-body bond-angle interactions were applied. Structural and dynamical properties of the simulated systems were evaluated and compared with experimental neutron diffraction, X-ray, Raman and infrared data. The structural characteristics of the samples are not very sensitive to the interaction potentials: in all cases, a continuous random network glass structure without any boroxol rings is generated. Experimental structural data are reproduced reasonably well. The dynamical behaviour of the glasses depends on both two- and three-body potentials. The two-body potentials, taken from literature, were reduced in order to obtain correct vibrational frequencies by multiplying all interaction potentials with a constant factor. Three-body interactions appear to be necessary for a satisfactory simulation of all vibrational modes in the glass network. Many features in the experimental spectra are reproduced surprisingly well.

STRUCTURAL AND DYNAMICAL PROPERTIES OF SOME LITHIUM BORATE GLASSES

Abstract Structural and dynamical properties of some lithium borate glasses have been investigated by means of X-ray diffraction studies and molecular dynamics (MD) calculations. The structure of lithium borate glasses appears to consist of randomly connected planar BO3 triangles and BO4 units. A comparison of the slowly quenched glasses (studied by X-ray diffraction) and fastly quenched glasses (studied by MD simulations) leads to the conclusion that a small quench rate leads to a preponderance for the B-O-B angles of adjacent BO3 triangles to 120°. The frequency spectra of B-O vibrations in the MD simulations agree qualitatively with infrared transmission spectra.

Luminescence and scintillation properties of BaY2F8 : Ce3+, BaLu2F8 and BaLu2F8 : Ce3+

Spectroscopic and scintillation properties of BaY2F8 :Ce3+, BaLu2F8 and BaLu2F8 :Ce3+ are presented. For pure BaLu2F8, a luminescence with a decay time of similar to 1 ns is observed under gamma-ray excitation. This luminescence with a light yield of about 200 ph/MeV is attributed to core-valence luminescence. The scintillation efficiency of the Ce3+-doped crystals is rather poor and usually smaller than 1000 ph/MeV. The scintillation mechanism of these fluorides will be discussed

Radiation damage of NaCl: dose rate effects

The authors discuss the experimental results on radiation damage of NaCl single crystals in terms of the Jain-Lidiard model. This model has been improved by taking into account the back reaction between F centres and Cl2 molecules. It appears that with this extended Jain-Lidiard model they can describe quantitatively the experimental data of Jenks and Bopp (1974, 1977). From the analysis they conclude that there should be appreciable dose rate effects, which is in agreement with the experimental results published by Levy et al. (1981). Depending upon the temperature and the total dose these does rate effects may cause very large concentrations of radiation damage. The low dose rate region (104 rad h-1) is of special interest, because the rocksalt in a nuclear waste repository is subjected to ionising radiation of this intensity for a long period of time. Until now no experimental information on radiation damage in NaCl has been available under these conditions. In the present paper they have calculated the concentrations of radiation damage under the above mentioned conditions within the improved Jain-Lidiard model. It appears that these concentrations may be up to about one order of magnitude larger than the ones observed by Jenks and Bopp, who have carried out their radiation damage experiments at dose rates between 107 and 108 rad h-1.

Assessment of the suitability of zircons for thermoluminescence dating

Abstract A suit of zircon (ZrSiO 4 ) samples has been selected for experiments by thermoluminescence (TL) and by Laser Ablation ICP-MS to study the role of rare earth elements (REE). It is shown that the trace element composition results for the heavy REE (HREE) are consistent, and that zircons are HREE enriched. In all sediment samples used in this work, we found significant concentration of Dy and Tb, which are the important activators for luminescence in zircon. At low temperatures, emission peaks due to Dy 3+ are dominant in the 3D-TL spectra while at high temperatures the Dy 3+ peaks are absent and the TL spectrum is dominated by the 6-line-Tb 3+ signal.