T. Ohgaku

Long-wavelength phonons and effective charges in complex perovskite compounds Ba(Mn1/3Ta2/3)O3 and Ba(Ni1/3Ta2/3)O3

The splitting of the polar modes into TO and LO components is due to the Coulombic field. The neutrality of the primitive unit cell and the independence of the external vibration modes from the internal ones lead to the present calculation. The higher frequencies for the internal vibrations related to tantalum ions than those related to manganese and nickel atoms observed in the two-mode behaviour also helped the consideration

Interaction between a dislocation and various divalent impurities in KCl single crystals

The strain-rate cycling test during the Blaha effect measurement at 77–254 K was carried out for four kinds of single crystals: KCl doped with Mg2+, Ca2+, Sr2+ or Ba2+ as a weak obstacle. It was found that the critical temperature, at which the effective stress is zero, increases when the divalent ionic size approaches increasingly that of the K+ ion. Furthermore, the activation energy for the interaction between a dislocation and the divalent ion-vacancy dipole was determined. The activation energy increases with the divalent ionic size. Fleischers model attributes this to the difference of tetragonality around the dipole for each specimen.

Plastic deformation of NaCl single crystal with superposition of ultrasonic oscillatory stress

A variation of deformation current as well as a reduction in static flow stress has been observed when an ultrasonic oscillatory stress was superimposed during the plastic deformation of NaCl single crystals. It is found that the activation volume can be estimated by two methods using the deformation current: one is from the stress amplitude and the other from the stress decrement at the removal of the oscillation. Good agreement has been obtained between experiment and theory by fitting these activation volumes to that obtained by the strain rate change test method. The dislocation velocity is found to increase with the aid of the oscillatory stress during the stress relaxation period.

Interaction between a dislocation and impurities in KCI single crystals

The strain-rate cycling test during the Blaha effect at 77–220 K has been carried out for three kinds of single crystals, KCI, KCI doped with Sr2+, and KCI doped with various impurities. The temperature and impurity dependence of the relation between strain-rate sensitivity and stress decrement, as well as the effective stress, τp1, due to only one type of impurity lying on the dislocation with the largest separation, has been investigated. From the temperature dependence of τp1, the force-distance profile between a dislocation and impurities was obtained. The critical temperature,Tc, for KCI: Sr2+ was found to be about 227 K.

Lattice vibration modes of (1 −x)Ba(Zn1/3Ta2/3)O3-xBaZrO3

Discussion de la variation des modes de vibration par addition des ions zirconium (x compris entre 0 et 0,04)

Investigation of interaction between a dislocation and a Cl− or I− ion in NaBr single crystals

Abstract Strain rate cycling tests were carried out under superimposition of oscillatory stress for NaBr single crystals doped with Cl − or I − . The relationship between strain rate sensitivity (SRS) of flow stress and stress decrement Δ τ due to superimposition of oscillatory stress is stair-like and consists of three regions, i.e. two plateau regions at low and high Δ τ and a middle region where the SRS decreases with increasing Δ τ . The stress τ p at the first bending point between the first plateau region and the middle one, which is considered to be the effective stress due to Cl − or I − , decreases with increasing temperature. The difference (SRS p ) between the SRS at the first and second plateau regions decreases with temperature. The SRS p is attributed to Cl − or I − . The interaction energies between a dislocation and a Cl − or I − are 0.40 or 0.47 eV in NaBr assuming that the force–distance profile is expressed by the Cottrell–Bilby relation. The force–distance profile is different from that for KCl:Br − .

Influence of a state of impurities on the interaction between a dislocation and impurities in KCl single crystals

The strain-rate cycling test during the Blaha effect measurement at 80 to 240 K has been carried out for two kinds of single crystals: quenched and annealed specimens of KCl:Sr2+. It was found that the force-distance profile, which expresses the interaction between a dislocation and impurities, cannot be approximated by the Fleischers model when I–V dipoles turn into aggregates for KCl:Sr2+, and that the activation energy for the break away of a dislocation from impurities becomes small for the annealed specimen, compared with the quenched one. Furthermore, the critical temperature,Tc, for the annealed KCl:Sr2+ is slightly smaller in comparison with that for the quenched one.

Study on the interaction between a dislocation and impurities in KCl : Sr2+ single crystals by the Blaha effect Part II Interaction between a dislocation and aggregates for various force-distance relations between a dislocation and an impurity

A strain-rate cycling test during the Blaha effect measurement was carried out at 83–239 K for the purpose of studying the force-distance relation between a dislocation and the aggregate for KCl : Sr2+ (0.05 mol% in the melt) single crystals. On the basis of the dependence of strain-rate sensitivity due to the aggregates on temperature, it was found that the interaction between a dislocation and the aggregate in the specimen can not be approximated to the Fleischers model taking account of the Friedel relation within the temperature. The square force-distance relation between a dislocation and an impurity seemed to be the most suitable model among the three: a square force-distance relation, a parabolic one and a triangular one, taking account of the Friedel relation for the specimen. In addition, the values of enthalpy and Gibbs free energy of activation for overcoming of the aggregate by a dislocation were obtained for the three force-distance relations.

Study on the interaction between a dislocation and impurities in KCl:Sr2+ single crystals by the Blaha effect Part III Influence of heat treatment on various characteristics

Strain-rate cycling tests associated with ultrasonic oscillation were conducted at 80–239 K for two kinds of KCl:Sr2+ (0.05 mol% in the melt) single crystals: quenched and annealed specimens. Examining the relationship of temperature and dislocation velocity-effective stress exponent, m*, estimated from the data obtained in this series, we could find the suitable force-distance relation between a dislocation and the impurity. The force-distance relation for the quenched specimen approached to the Fleischers model taking account of the Friedel relation rather than the Fleischers model. As for the annealed specimen, the SQ was the most appropriate of the three models: the SQ, the PA, and the TR indicate a square, a parabolic, and a triangular force-distance profile respectively. The three force-distance relations are taken account of the Friedel relation. By annealing the quenched specimen, m* became low at a given temperature. This may have been caused by the following two phenomena. First, the concentration of weak obstacles to dislocation motion decreased after the heat treatment. Secondly, the resistance to movement of a dislocation in the quenched specimen was weakened by annealing it, e.g., F0 was reduced to about one-third and ϕ0 increased from 154 to 172 degrees. F0 and ϕ0 are the force acted on the dislocation and the bending angle of dislocation by the weak obstacle such as the impurity. Therefore, it may be deduced that the dislocation velocity in the quenched specimen is more sensitive to the effective stress due to the impurities than that in the annealed specimen at the temperature.

ESR study for a TSEE peak in X-irradiated Li2B4O7:AgCl crystallized glass

Thermally stimulated exoelectron emission (TSEE) from X-irradiated crystallized glass of Li2B4O7 doped with 0.03 mol% AgCl showed a conspicuous peak at 155° C, which is absent in an undoped sample. ESR analysis of the samples revealed that Ag0 atoms which had been formed by X-irradiation are responsible for the 155° C TSEE peak.