A microstructure causing the memory effect in the incommensurate phase of barium sodium niobate was investigated by means of a transmission electron microscope. A type of microdomain structure, which is constituted of a complicated array of microscopic ferroelastic domains with a modulation along the [100] direction, is found. Because this microdomain structure appears reversibly during the heating and cooling processes, the microdomain structure is directly related to the memory effect.

The amount of lithium, ${\mathit{x}}_{\max }$, which can be intercalated in a graphitic carbon host is affected by the amount of turbostratic disorder in the host. Using electrochemical methods, we show that ${\mathit{x}}_{\max }$ in ${\mathrm{Li}}_{\mathit{x}\max }$${\mathrm{C}}_6$ is given by ${\mathit{x}}_{\max }$=1-P, where P is the probability of finding a random rotation or translation (turbostratic disorder) between adjacent graphite layers, implying that the interlayer spaces or galleries between randomly stacked layers do not host lithium ions. These ‘‘blocked ’’ galleries influence the staged phases and the compositions of stage-1 (${\mathit{x}}_{\max }$) and stage-2 (${\mathit{x}}_{2\mathrm{m}\mathrm{a}\mathrm{x}}$) materials. A simple model is proposed to explain the variation of the composition of the stage-2 phase, ${\mathit{x}}_{2\mathrm{m}\mathrm{a}\mathrm{x}}$, with P.

A series of sodium polyphosphate glasses of composition ${\mathrm{Na}}_{\mathit{n}+2\mathrm{}}$${\mathrm{P}}_{\mathit{n}}$${\mathrm{O}}_{3\mathit{n}+1\mathrm{}}$ have been studied using synchrotron-radiation x-ray-absorption spectroscopy. High-resolution P L-edge and K-edge x-ray appearance near-edge structure (XANES) as well as K-edge extended x-ray-absorption fine structure (EXAFS) of the phosphates have been investigated. It has been found that while the K-edge XANES spectra of different phosphate glasses are similar, the L-edge XANES features are strikingly different. These results show that the intensities of the low-energy spin-orbit doublet in the P L-edge spectra increase with average chain length of polyphosphate glasses. The increase is very rapid up to n=20, then it levels off as the chain length increases above this value. Using this information, a quantitative calibration curve has been established which can be used to determine the chain length of polyphosphates in bulk or surface films. The features observed in the XANES spectra of the polyphosphates have been assigned. From EXAFS measurements, the average bond distances and coordination numbers around P have been measured. It was found that within the accuracy of EXAFS, average P-O bond distances in polyphosphate glasses do not change substantially.

Using extended x-ray-absorption fine-structure (XAFS) spectroscopy we have determined the radii of the first three atomic shells around Ga and the first Pu shell in a fcc Pu alloy stabilized by 1 wt. % Ga. We find the Ga to be substitutional in the fcc lattice, with the first and second shells contracted by 3.7 and 0.9%, respectively, relative to distances expected from the lattice constant derived from x-ray diffraction. The lattice is well ordered around Ga, but there is considerable static disorder in all observed coordination shells of Pu. We discuss these results in relation to the mechanism by which Ga effects phase stabilization.

The formation of amorphous ${\mathrm{LiBO}}_2$, as well as its particle size and phase-transition mechanism, have been investigated by means of thermal analysis, transmission electronic microscopy (TEM), and high-temperature and normal-temperature x-ray-diffraction analyses. ζ, η, and θ phases of ${\mathrm{LiBO}}_2$ have been observed in the crystallization process of the dehydrated amorphous ${\mathrm{LiBO}}_2$, which cannot be observed during the crystallization process of glassy ${\mathrm{LiBO}}_2$. Unlike noncrystalline glass, the crystallization process of the dehydrated amorphite is dependent on the dehydration conditions. This can act as an approach to synthesize new materials.

Optical gyration G, birefringence Δn, and their electric-field E dependences of transparent ceramics of ${\mathrm{Pb}}_{0.92}$${\mathrm{La}}_{0.08}$(${\mathrm{Zr}}_{0.70}$${\mathrm{Ti}}_{0.30}$${)}_{0.98}$${\mathrm{O}}_3$ were studied by using high accuracy universal polarimeter in a temperature range between -10 °C and 90° C. The high-temperature phase manifested neither spontaneous nor induced G by applying the biasing E, while the low-temperature phase did characteristic hysteresis loops of G, and Δn with respect to E. Group-theoretical consideration of gyro-optical properties of both phases led us to the conclusion that the high- and low-temperature phases are cubic ${\mathit{T}}_{\mathit{h}}$ and trigonal ${\mathit{C}}_3$. They transform into each other at ${\mathit{T}}_{\mathit{c}}$=10.3 °C with essentially second but apparently first order. The free-energy function which drives the transition was determined by using electro-optic phenomena occurring in the phase-transition region. Calculated and observed values of G and Δn as a function of E were in excellent agreement in the transition region. However, they began to deviate from 50 °C and the deviations became serious above 80 °C. Brief comments are given on the anomalous dielectric behavior of lanthanum modified lead zirconate titanate ceramics.

The velocity dependence of the stopping power of a two-dimensional noninteracting electron gas for heavy in-plane ions is calculated. The transport cross section required in the kinetic treatment is determined for a bare Coulomb potential. Detailed analytical and illustrative numerical results are derived. The problem of screening is also discussed.

The low-temperature phase transformation in a Li–10 at. % Mg bcc single crystal is investigated by neutron-scattering techniques. A mild phonon softening of the ${\mathrm{TA}}_1$[110][11¯0] phonon branch is observed on cooling. This softening is most pronounced at reduced q values near 1/3[110] of the bcc lattice. The close-packed low-temperature phase was found to have the 9R structure over its entire range of stability in contrast to more complicated structural features occurring in the pure alkali metals.

In this paper we derive expressions for the laser slope efficiency and the threshold absorbed pump power which explicitly include excited-state absorption in the pump as well as in the laser-emission-wavelength domains. They are applied to the case of the diode-pumped ${\mathrm{Nd}}^{3+}$-doped laser systems and, along with expressions allowing the calculation of excited-state-absorption (ESA) cross sections within the framework of the Judd-Ofelt theory, they provide a theoretical framework for the second part in which we present both experimental measurements and theoretical calibrations and an analysis of excited-state-absorption spectra in the stimulated emission as well as in the pumping domains of ${\mathrm{Nd}}^{3+}$-doped ${\mathrm{Y}}_3$${\mathrm{Al}}_5$${\mathrm{O}}_{12}$, ${\mathrm{YLiF}}_4$, and ${\mathrm{LaMgAl}}_{11}$${\mathrm{O}}_{19}$ laser crystals. The results indicate that ESA in the infrared metastable state of ${\mathrm{Nd}}^{3+}$ in these materials is negligible at the main laser wavelengths but can be more significant if it takes place, following some energy-transfer induced-excitation process, in higher-lying excited states. The analysis of these ESA within the Judd-Ofelt formalism shows a general agreement better than 50% between the experimental data and the theoretical predictions. This is used to estimate the influence of ESA in the pumping domain on the laser performance of the materials. It is found that it contributes but that it does not significantly perturb this laser performance, and that this effect is much less than some upconversion energy transfers that limit the fluorescence excitation efficiencies and reduce the energy-storage capacities by the reduction of the effective fluorescence lifetimes of the laser metastable level.

Results are presented on the multisite structure of ${\mathrm{Nd}}^{3+}$ in YAG, obtained from a comparative study of melt-grown high-temperature (HT) and flux-grown (F) crystals by using optical spectroscopy in connection with x-ray data. Absorption and emission data by pumping into ${}_{}{}^4{}_{}{}^{}$${\mathit{G}}_{5/2}$, ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{9/2}$, and ${}_{}{}^4{}_{}{}^{}$${\mathit{G}}_{7/2}$ ${\mathrm{Nd}}^{3+}$ multiplets are presented; very good resolution is obtained for pumping into ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{9/2}$. The optical spectra show three types of centers: centers present in all samples, centers present mainly in the HT crystals (and very weak in F samples), and minor or irregular centers. Besides the main center (${\mathrm{Nd}}^{3+}$ in isolated dodecahedral c sites) all samples contain three satellites, assigned to ${\mathrm{Nd}}^{3+}$(c)-${\mathrm{Nd}}^{3+}$(c) pairs in the first, second, and third coordination spheres. A model is proposed to explain the pair lifetimes and their dependence on Nd concentration by assuming a superexchange interaction for the nearest-neighbor pair and electric dipole coupling for the other pairs. Three satellites of equal intensities, observed in the HT samples (and very weak in the F crystals), are connected with the crystal-field perturbations at the c sites produced by an excess of ${\mathrm{Y}}^{3+}$ ions in octahedral a sites, as predicted by the nonstoichiometry data. This result is consistent with the very weak intensity and with the systematic equivalence of the {222} forbidden reflections in our x-ray data, obtained only in the HT crystals. Arguments are given that these satellites are involved in cross-relaxation processes similar to those of the main center. The spectral features of a center that dominates the low-temperature ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{3/2}$ emission under pumping at 532 nm are also analyzed.

We report theoretical and experimental results demonstrating covalent bonding between ${\mathrm{C}}_{70}$ molecules. Experimental results indicating the transformation of ${\mathrm{C}}_{70}$ films upon exposure to visible or ultraviolet radiation into a strongly bonded solid phase, similar to the transformation observed in solid ${\mathrm{C}}_{60}$ films are presented. Unlike ${\mathrm{C}}_{60}$ molecules, however, the covalent bonding between ${\mathrm{C}}_{70}$ molecules is found to be highly directional, strongly favoring certain relative intermolecular orientations. This theoretical finding is consistent with recent laser desorption mass spectroscopy results for visible or UV light irradiated ${\mathrm{C}}_{70}$ films which find the cross section for the phototransformation to a new toluene-insoluble solid phase to be considerably smaller than observed for solid ${\mathrm{C}}_{60}$. The combined results suggest that the photochemical 2+2 cycloaddition reaction is responsible for the transformation.

The experimental As K-edge x-ray-absorption fine structure of ${\mathrm{As}}_2$${\mathrm{S}}_3$ is analyzed in detail and compared to data calculated theoretically from a model structure. The experimental spectrum is resolved into two components, one representing a bound excited state resonance and a second due to transitions to the continuum. The bound state resonance is located 6.1 eV below the continuum threshold and is fitted by a Lorentzian. The continuum structure is constructed using theoretically calculated χ and absorption cross section data together with an arctangent function simulating the absorption and lifetime at the continuum edge. For the theoretical calculation, the ab initio code feff was applied to an atomic cluster representing the amorphous solid. The results show that multiple scattering effects give rise only to small contributions in the region of the continuum threshold. They are negligible for higher energies.

The radiative corrections to the Compton scattering cross section have been studied to deduce their importance in a momentum-density measurement for accurate analysis of solid-state physics. The uncertainty introduced by the infrared divergence of radiative correction and double Compton scattering is discussed and analyzed in a model system resembling aluminum metal. The radiative correction has been found to be very small in the energy range (E≲2.5 MeV) useful for solid-state physics experiments but not completely negligible.

The coherent dynamics of atomic tunneling states in (KBr${)}_{1\mathrm{-}\mathit{x}}$(KCN${)}_{\mathit{x}}$ crystals in the concentration range 0.001≥x≥0.18 have been investigated at low temperatures with two types of dielectric echo experiments at 800 MHz. In rotary echoes we find a distribution of the Rabi frequency which is very narrow in comparison with corresponding results from structural glasses. This shows that the distribution of tunnel splittings in (KBr${)}_{1\mathrm{-}\mathit{x}}$(KCN${)}_{\mathit{x}}$ differs significantly from that in amorphous materials. At least from this point of view, it is doubtful whether (KBr${)}_{1\mathrm{-}\mathit{x}}$(KCN${)}_{\mathit{x}}$ can be considered a model system for the low-temperature properties of the tunneling states in glasses. In addition we have investigated the temperature dependence of the phase memory and of the energy relaxation time of the tunneling states by studying the decay of the spontaneous and the stimulated echo in two- and three-pulse echo experiments.

We investigate several consequences of the atomic size effect in crystalline III-V alloys by performing numerical calculations in the framework of the extended valence-force-field model and we compare our results with available experimental data. First, we demonstrate the existence in these alloys, even if they are fully disordered, of large anisotropic spatial correlations between the static atomic displacements from the sites of the average sublattices, and we calculate the corresponding correlation functions. Second, we show that these very correlations induce a previously unrecognized characteristic contrast in the conventional transmission-electron-microscopy images of such alloys. We explore the behavior of this atomic-size-effect contrast upon changing the diffraction conditions. These results are obtained by simulating large alloy supercells and by subsequently performing dynamical image calculations. Finally we compare qualitatively and quantitatively our calculated contrast with the fine-scale contrasts observed in the experimental micrographs of these alloys.

A comparative study of electron-beam and pulsed-laser irradiation effects in metallic glasses has been performed in order to understand the relationship between magnetic behavior and select variations in the structural characteristics of alloy phases. Samples of ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$ metallic glass were irradiated with a pulsed excimer laser (λ=308 nm, τ=10 ns), with a high-energy electron beam (W=7 MeV), and with low-energy electron beams (W=30 and 50 keV). Irradiation-driven changes in the magnetic anisotropy and phase equilibrium of alloy samples were studied by Mössbauer spectroscopy and scanning electron microscopy. Complementary information was obtained using energy-dispersive x-ray analysis. High-energy electron-beam irradiation was found to induce an out-of-plane magnetic anisotropy due to changes in the chemical short-range order. Low-energy electron-beam irradiation resulted in the formation of crystalline regions, in which α-Fe, Fe-Si, ${\mathrm{Fe}}_3$B, ${\mathrm{Fe}}_2$B, and clusters of γ-Fe were identified. Interpretation of these results is given in terms of radiation-enhanced diffusion. Pulsed-excimer-laser irradiation was found to induce controlled magnetic anisotropy without onset of bulk crystallization in the ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$ amorphous system. The effect of excimer-laser-induced amorphization was evidenced in thermally annealed ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$ samples and explained using melt model calculations. In all cases studied, the key to explaining the irradiation-induced property modifications is the underlying alloy microstructure.

The glass structure and physical properties are reported for the nonconventional binary bismuth cuprate glasses of compositions (CuO${)}_{\mathit{x}}$(${\mathrm{Bi}}_2$${\mathrm{O}}_3$${)}_{100\mathrm{-}\mathit{x}}$, for x=27–70 mol %, prepared by the roller-quenching technique. It has been observed that stable glasses with nearly the same topology can be obtained in this system for a larger composition range compared to the multicomponent bismuth cuprate glasses. The network structure is built up of [${\mathrm{BiO}}_3$] pyramidal units. The strength and connectivity of the glassy network increase at nearly equimolar glass composition. The nearly equimolar glass composition crystallizes to tetragonal ${\mathrm{Bi}}_2$${\mathrm{CuO}}_4$ crystal. The appearance of hyperfine structure in the ESR line shapes for the glass compositions with high CuO content is not clear at this moment.

In this work the problem of the prediction of the external shapes (habits) of icosahedral quasicrystals is addressed in terms of geometrical considerations. The cut and projection method is used to find the densest family of quasilattice planes that, according to the Bravais rule, are the most significant from the morphological point of view. The three kinds of six-dimensional cubic lattices are worked out, namely, primitive (P), face centered (F), and body centered (I). Algebraic methods are proposed to find the densest sublattices of the six-dimensional lattices projecting onto a given quasilattice plane. The results are compared with experimental observations.

Metastable γ-${\mathrm{FeSi}}_2$ fluorite-type was formed as precipitates in Si(100) by room-temperature ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ implantation, followed by ion-beam-induced epitaxial crystallization at 593 K. In spite of the cubic structure of γ-${\mathrm{FeSi}}_2$, the Mössbauer spectrum consists of two broad lines, rather than a single line. It is best described by means of a smooth distribution of electric field gradients with nearly the same isomer shift (${\mathrm{\delta }}_{\mathrm{IS}}$=0.198 mm/s) for each gradient. After thermal treatments at 773 K the distribution narrows and a finite probability occurrence frequency for zero gradient appears. As the structure of ideal γ-${\mathrm{FeSi}}_2$ consists of Si cubes alternately filled with Fe atoms, it is suggested that the distribution arises from misplacement of Fe atoms to empty Si cubes in the lattice. The dependence with thermal treatments and the evolution towards β-${\mathrm{FeSi}}_2$ are discussed.

We have addressed the problem of dynamical localization in a one-dimensional system with a periodic potential incommensurate with the crystal lattice under the action of a dc electric field. For the chosen potential there exists a mobility edge, that is, a critical value of the ratio between the strength of potential to the half bandwidth η=${\mathrm{\epsilon }}_0$/2V, which classifies the nature of the wave functions. We show that the effect of the field is to shift the mobility edge towards the delocalized region. We show that the field influence on localization is much stronger than that due to the disorder. It is also shown that when a resonance condition is reached the wave packet oscillates with a characteristic frequency in the terahertz range for superlattices, such an effect can be used to generate electromagnetic radiation of this frequency range.