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Ultrasonic velocity and internal friction measurements on a single crystal of Bi2Sr2Ca1Cu2Ox grown by directional solidification have shown a number of anomalous features and instabilities which correlate well with annealing treatments designed to change the oxygen concentration. It is suggested that a first-order phase change occurs close to 150 K in crystals annealed under vacuum conditions.

Experimental results are presented for the ultrasonic velocity and attenuation of shear waves at 2.4 MHz in proustite. The effects of the polarization and wavelength of irradiation in the range 450-900 nm on the photoinduced phase transition at 210 K are reported.

The previous work on the topic of phase transitions in proustite is briefly reviewed. Study on the fundamental absorption edge related optical properties of proustite is reported, which reveals anomalies in the average absorption coefficient, band gap energy and polarization shift at temperatures near 210 K. These anomalies together with the abnormal photodielectric behaviour observed in this study provide conclusive evidence for the existence of the photoinduced broad phase change near 210 K. The nature of this photoinduced phase change is assumed to be a displacive type ferroelectric phase transition with a relative displacement of the two sublattices resulting from the redistribution of silver ions under the action of illumination and cooling near to the phase transition temperature.

The ultrasonic attenuation in proustite has been measured in the vicinity of 210 K. the results provide further evidence for a photoinduced phase transition at this temperature. A possible mechanism for the increase in attenuation induced by illumination is discussed.

The temperature dependent ac conductivity of single‐crystal proustite measured at several frequencies over the temperature range from 82 to 467 K reveals six distinct regions associated with different conduction mechanisms. A phase transition from ionic to superionic conduction has been found to occur at a temperature of approximately 420 K. The frequency dispersion spectra obtained at different temperatures from 82 to 373 K, over the frequency range 10−2 to 103 Hz show two regions of frequency dependent conductivity. The dc conductivity and ionic hopping rate as well as the carrier densities have been extracted from the ac conductivity data. The results show that the ac conductivity of proustite is characterized by low hopping rates and high carrier densities suggesting that the Ag+ ions may execute a long range hopping motion in the lattice. The relationship between the dc and ac components of conductivity have been critically examined and the results show that the ratio σdc/σac is thermally stimulated ...

The parameters controlling the intergranular percolating network of the new class of high temperature superconductors have been studied using a novel method to control specimen composition as the percolation limit is approached. The form of the resistive transition in two-phase composites formed from Y2BaCuO5 and YBa2Cu3O7-δ is shown to be complex and that processes occuring in each of a number of temperature ranges are discussed. Microbridges formed from these materials show characteristics which are determined by the weak-link structure and display features related to the resistive transition of the bulk material.

The Faraday rotation and MCD spectrum about absorption bands in erbium-doped soda glass have been studied. The measurements were made in the saturation region and the g-value of the 4I15/2 ground state determined by use of the method of moments. The dominant nature of C-terms in rare-earth doped glasses are confirmed and the Faraday parameters derived for all optical transitions. Some comments are made on the existence of trigonal and tetragonal sites for the erbium ion in the glass matrix. By selective doping with erbium it is possible to produce a glass that has a zero Verdet constant.

The electrical resistivity of double hexagonal close-packed Pr-Ce alloys containing up to 25 at. % Ce has been studied in the temperature range 1·3—300 K. In addition to the usual divergence at T = 0 K. evidence has been found of structure at about 20 and 90 K. This is tentatively ascribed to the presence of Kondo sidebands of the type discussed by Maranzana and is related to the cerium crystal field levels expected in the alloys on the basis of Rainford's (1971) crystal field parameters for pure Pr. Evidence has also been obtained under certain conditions for the existence of anti-ferromagnetic ordering in the alloys at around 26 K. similar to that observed in pure Pr by Meaden and his co-workers (1972).

Ellipsometric measurements have been made of optical properties of the heavy rare earth metals Gd, Tb, Dy, Ho, Er in the phonon energy range 0.35 eV to 2.5 eV and at certain temperatures between 20K and 300K corresponding to various magnetic phases of the metals. Rather diversive optical behaviour of the metals below the ordering temperature is interpreted in terms of exchange splitting of the levels near the Fermi level causing their reoccupation.

Observations of the polarisation-sensitive optical absorption in single-crystal proustite have been made over the temperature range from 82 to 460 K. By combining the data obtained from a number of samples of varying thickness the complete absorption spectrum has been found for absorption coefficients of up to approximately=2*104 cm-1. The experimental results show that the optical inter-band transitions are dominated by indirect processes up to photon energies of about 3 eV. The phonons involved in these transitions have been tentatively identified. Deviations from the simple indirect transition scheme at high absorption coefficients are attributed to additional indirect transitions to higher branch conduction band minima. A possible schematic band structure is suggested close to the Gamma point.

Ultralow‐frequency (10−2–103 Hz) electrical conductivity and dielectric constant measurements have been made on single‐crystal proustite at room temperature under various illumination conditions. An unusual phenomenon of frequency‐dependent negative photoconductivity and negative photocapacitance was observed at very low frequencies. We believe that both these negative photoeffects can be attributed to space‐charge effects and the results are interpreted using a two‐layer dielectric structure model.

The magnetic and structural properties have been examined for pseudobinary compounds for many stoichiometries and solubility ranges in the phase diagrams defined by Y(Fe, Co) and Y(Co, Ni). Attempts have been made to account for the disappearance of certain phases in terms of atomic substitution and changes in the electron concentration. The magnetic behaviour is related to that of the alloys of the pure metals iron, cobalt and nickel; however a deep minimum is found to occur in the molecular moment in several stoichiometries near to the nickel compound. There is also a corresponding minimum in the exchange interaction strength. The observations may be understood in terms of an analysis involving the form of the density of states curves in these materials.

Resistivity measurements are made on a number of light-heavy rare-earth alloys in the temperature range 2.7 to 300 K. The influence of the magnetic structure on the residual resistivity, ϱres, the spin-disorder resistivity, ϱs-f, and the Neel temperature, TN, is discussed for the range of compositions studied. The influence of alloy composition on conduction electron effective mass is considered. [Russian Text Ignored].

Lynds 1642 is a small, somewhat insignificant dark cloud centred at 04h33, — 14°20 (1950). On a IIIaJ UKSTU Schmidt plate it may be seen to lie within an approximately circular patch of nebulosity which we believe to be visible by reflection. Its galactic location (l = 210°.9 b = -36°.5) places it beneath the local arm in the direction of Orion and it is likely that it is seen by reflection of the integrated light of the stars in that region of the galaxy.

Calculations previously made for α-zirconium are extended to determine how the introduction of rhodium into zirconium affects the energy of absorbed interstitial hydrogen. The predicted change in energy of 0.05 Ryd on alloying is in reasonable agreement with the estimated experimental result. Fruher fur α-Zirkon durchgefuhrte Rechnungen werden erweitert, um zu bestimmen, wie die Einfugung von Rhodium in Zirkon die Energie von absorbiertem-Zwischengitterwasserstoff beeinflust. Die vorhergesagte Energieanderung von 0,05 Ryd nach dem Legieren befindet sich in vernunftiger Ubereinstimmung mit dem berechneten experimentellen Ergebnis.

Method of estimating the free electron contribution to the optical conductivity for the heavy rare earths is presented. [Russian Text Ignored].

Measurements of the shielding effectiveness of yttrium barium cuprate have shown that at low signal amplitudes the insertion loss is significant over a wide frequency range. The performance, however, is extremely sensitive to the signal amplitude and to the presence of local static fields. The major contribution to the shielding arises from reflection at the sample surfaces due to the impedance mismatch. An absorption component also exists which is associated with energy loss processes involving the breaking of weak‐link intergranular contacts which allow flux to move into and through the material. These effects are closely related to the nonlinear magnetic properties of these superconductors which also lead to the appearance of a rich harmonic content in the transmitted waveform. While these effects are not encouraging for the use of these materials as shields, the suggestion is made that they could form the basis of a new class of frequency upconverters and mixers for high‐frequency communication.

The variation of the electrical resistivity with temperature in the range 2.7 to 200 K is measured for four light–heavy rare-earth alloys, i.e. PrTb, NdDy, NdY, and LaDy. The discussion of the resistivity behaviour can be divided into three parts corresponding to the three crystallographic phases in which these alloys crystallize at room temperature and below, i.e. d-hex, Sm-like and h.c.p., in the direction from the light to heavy rare earth. [Russian text Ignored.]

The Faraday rotation and MCD spectrum about absorption bands in neodymium-doped soda glass have been studied at temperatures below 100K. The saturation behaviour of the Faraday rotation at 4.2K was studied, with the ground state g value being determined. Comments on local ordering in the glass are also made. The MCD spectrum was analysed using the method of moments and the relative contributions of the A and C terms to the MCD dispersion ascertained. The Faraday parameters are derived for all optical transitions.

Neutron diffraction experiments indicate that hydrogen enters α-zirconium interstitially. The relative energies of hydrogen in tetrahedral and octahedral interstitial sites of the h. c. p. lattice are calculated assuming that the energy terms most strongly dependent on the site symmetry are the electronic and protonic electrostatic contributions. The calculations show that the tetrahedral site is preferrred, in agreement with experiment. The effects of lattice distortions near a proton are shown to be unimportant in determining the site preference. Neutronenbeugungsexperimente zeigen, das Wasserstoff in α-Zirkon Zwischengitterplatze besetzt. Die relativen Energien von Wasserstoff in tetraedrischen und oktaedrischen Zwischengitterplatzen des h. d. p.-Gitters werden unter der Annahme berechnet, das die am starksten von der Platzsymmetrie abhangenden Energieterme die elektrostatischen elektronischen und protonischen Beitrage sind. Die Rechnungen zeigen, das der Tetraederplatz bevorzugt wird in Ubereinstimmung mit dem Experiment. Es wird gezeigt, das die Einflusse von Gitterverzerrungen in der Nahe eines Protons bei der Bestimmung der Platzbesetzung unwesentlich sind.

The Faraday rotation and MCD spectrum about absorption bands in praseodymium- and holmium-doped soda glass has been studied at temperatures less than 100K. The MCD spectrum was analysed by the method of moments and the relative contributions of the A, B and C terms obtained, it being found that C terms dominate in rare-earth-doped glasses. The Faraday parameters are derived for all optical transitions and the rare-earth site in the glass matrix is shown to be trigonal by interpretation of the sign of the C terms. Brief comments on the g-values of the bound states are made in relation to crystals of similar symmetry. It is also suggested that these glasses may find application in magneto-optical devices.

On a observe un nuage d'hydrogene neutre, lineairement etendue, de faible masse, au voisinage de UW CMa. Sa structure et son champ des vitesses suggerent qu'il est associe a UW CMa. ON envisage plusieurs modeles pour rendre compte de cette relation

On a decouvert un petit amas d'etoiles jeunes, obscurcies autour de RCA. Les couleurs IR de ces etoiles sont en accord avec l'hypothese selon laquelle il s'agirait d'etoiles pre-sequence principale recemment formees. On suggere la denomination «Coronet» pour ce nouvel amas

The phonon spectrum of YBa2Cu3Oy depends on the oxygen concentration. With decreasing oxygen content and LO mode at 655 cm-1 increases rapidly while the mode content between 220 and 400 cm-1 decreases. These changes are accompanied by an equally rapid increase of a band of TO modes between 230 and 365 cm-1. The feature at 655 cm-1 may be associated with an A2u mode involving asymmetric Cu-O motion parallel to the c axis. Removal of the chain oxygen atoms reduces the damping of this motion and allows the A2u mode to grow while leading to a redistribution of phonon energy from LO to TO modes below 300 cm-1.

The band structures of zirconium hydride compounds are calculated using the APW method. By comparing the bands for a hypothetical f.c.c. compound ZrH0 with f.c.c. ZrH2 (corresponding to the Δ-phase), it is shown that the hydrogen atoms give rise to a new ‘bonding’ band below the Fermi level. The band structures of two interstitial hydrogen h.c.p. compounds ZrH0.5 and ZrH (α-phase) are also calculated. For ZrH0.5 with two Zr atoms and one H atom in the primitive unit cell no new bands are formed. For ZrH with two Zr atoms and two H atoms in the primitive unit cell a new band is formed just below the Fermi level but the band structure is similar to that of ZrH0.5 and a-Zr with the Fermi level raised. Estimates of the total energies show that the band structure contributions favour formation of f.c.c. ZrH2 (corresponding to the Δ-phase) over an interstitial α-phase, as is observed experimentally. Mit der APW-Methode werden die Bandstrukturen von Zirkonhydridverbindungen berechnet. Durch Vergleich der Bunder fur eine hypothetische k.f.z.-Verbindung ZrH0 mit kf.z.-ZrH2 (ent-sprechend zur δ-Phase) wird gezeigt, das die Wasserstoffatome Anlas zu einem „bindenden” Band unterhalb des Ferminiveaus geben. Die Bandstrukturen von zwei Zwischengitterwasser-stoff-h.d.p.-Verbindungen, ZrH0.5 und ZrH (α-Phase), werden ebenfalls berechnet. Fur ZrH0.5 mit zwei Zr-Atomen und einem H-Atom in der primitiven Einheitszelle werden neue Bander gebildet. Fur ZrH mit zwei Zr-Atomen und zwei H-Atomen in der primitiven Einheitszelle wird ein neues Band genau unterhalb des Ferminiveaus gebildet, jedoch ist die Bandstruktur der von ZrH0.5 und α-Zr mit angehobenem Ferrniniveau ahnlich. Berechnungen der Gesamtenergien zeigen, das die Bandstrukturbeitrage die Bildung von k.f.z.-ZrH2 (entsprechend zur Δ-Phase) gegenuber einer Zwischengitter-α-Phase bevorzugen, wie experimentell beobachtet wird.

Measurements of the complex dielectric constant of single-crystal proustite over the frequency range 10-2-5*106 Hz have shown the presence of a temperature-dependent relaxation process with characteristic times of between 1*10-2 and 6.5*10-4 s. Three activation energies are observed in the resistance measurements which correlate with reported phase transitions in this material. The dielectric relaxation can be interpreted in terms of a combined model, in which the 'Universal' dielectric dispersion law describing the anomalous low-frequency behaviour is combined with a two-layer Maxwell-Wagner model to account for the relaxation processes. The limited dielectric properties of the material have been established.

The Corona Australis cometary globule is a large southern object known to be a region of slow star formation. We have mapped the complex in the 21cm hydrogen line and preliminary results are reported in Llewellyn et al. (1981) and Taylor et al. (1981). The most extensive A, map of the region is given by Rossano (1978) and is based on star counts.

Torque measurements have been made on single‐crystal dysprosium. The constant K1 was determined in the paramagnetic region, and also in the antiferromagnetic region, where the transition to ferromagnetism appeared as a large distortion in the torque curves. From the data in the paramagnetic region the saturation value of K1 is predicted as 1.1×108 ergs g−1. The constant K4 was determined in the ferromagnetic region, and changes in sign were observed at field strengths close to the critical value. The changes in easy direction for magnetization are compared with the behavior of the magnetostriction of dysprosium.

The optical properties of terbium doped soda glass have been investigated as a function of terbium concentration. The properties studied in this work were the excitation luminescence and absorption spectra and the luminescence decay times. In the case of short wavelength excitation, the absorption occurs in the glass matrix and is followed by energy transfer to the Tb3+ ions. At long wavelengths the efficiency of energy transfer between Tb3+ ions by dipole-dipole interaction is small up to quite high concentrations of terbium in the glass. However, above approximately 1 wt.%Tb the intensity of the luminescent 5D4 to 7Fj transitions increases very rapidly with terbium concentration. It is suggested that in this range energy transfer occurs between the ions of a Tb3+ ion pair by means of an exchange-dipole interaction.

Measurements have been made of the structural and magnetic properties of a series of pseudobinary compounds based on Gd3Co. The results have been interpreted in terms of the Neel theory of metamagnetism and the various exchange interaction coefficients have been obtained.

Measurements of the electron spin resonance spectrum have been made in a Gd3+ doped lithium-aluminium-silicate glass at various stages during the crystallization of the glass. The crystallization was induced by heat-treatment at various temperatures and took place either from the surface or from nucleation centres produced by the presence of TiO2 in the glass. The changes in the resonance spectra have been interpreted in terms of the stability of the gadolinium sites. In the presence of titanium, it is suggested that complexes are formed in the glass which involve both titanium and gadolinium ions. Supporting measurements show that the presence of these complexes is also detectable from the more conventional structural and thermal characterization of the glasses.

The magnetic and structural properties of the neodymium- dysprosium alloy system have been measured over the entire composition range. The crystal structures change from hcp to Sm type to dhcp arrangement with increasing neodymium concentration. Magnetization and initial susceptibility measurements suggest that the dhcp phase does not order magnetically. In the Sm phase antiferromagnetic behaviour is observed while the hcp alloys show a step ordering process. The Neel points follow a 2/3 power law variation with a reduced de Gennes function G given by the difference of the de Gennes functions for the two components of the alloy.

Measurements of the magnetocrystalline anisotropy constants have been made on a single crystal of gadolinium using a torque magnetometer. The apparatus used is briefly described and the application of corrections for lack of saturation and for a paramagnetic component are explained. Measurements have been made between 37.5 °K and 315 °K and it is found that three constants are required to represent the results. It is shown that at temperatures greater than 240 °K the easy direction is the hexagonal axis. Below this temperature the easy direction lies on a cone whose axis is the c axis, and the variation of cone angle with temperature is calculated from the values of the anisotropy constants.

The effects of both static and alternating electric fields on scintillations produced by alpha particles in zinc sulphide have been examined. The results indicate that in electroluminescent crystals the brightness is reduced when the alpha particles are incident on the negative electrode. A change of barrier thickness with frequency was estimated from the results. The variation is interpreted as a change in dielectric constant with frequency. The results aeo in good agreement with earlier work and are supported by observations of the electroluminescence threshold voltage.

The magnetic properties of the series of pseudo-binary compounds YFeuCo2-u have been examined in an attempt to obtain further information concerning the nature of the transition-metal moment in the cubic Laves-phase rare-earth - transition-metal compounds. The variation of the observed moment throughout the series can be understood on the basis of a non-localized moment associated with the transition-metal ion. The variation of the Curie temperature may be associated with the variation of the lattice parameter between the terminal compounds.

Measurements have been made of the magnetic ordering temperatures and spontaneous moments in the pseudobinary systems Y(Co, Ni)3 and Y2(Co, Ni)7. The results have been interpreted in terms of a rigid band model and it is suggested that the magnetic behaviour of YNi5 follows directly from the same band structure.

The hyperfine fields at the 59Co nucleus have been observed in GdCo2 (GdY)Co2, (GdDy)Co2 and Gd(CoNi)2 using a spin echo technique. The field strength in the basic compound GdCo2 was found to be 607 kOe. The results can be interpreted in terms of contributions to the hyperfine field arising from the transition metal sublattice and from the rare earth sublattice. The former appears to be proportional to the magnetic moment associated with the transition metal ion while the rare earth contribution is taken to arise predominantly from conduction electron polarization. With yttrium substitution this second term is found to be directly proportional to the gadolinium concentration. In the nickel substituted compounds the hyperfine field due to the rare earth sublattice is observed to decrease. This is believed to be the result of a change in conduction electron concentration.

An attempt has been made to account for the existence of the crystallographic phases observed in the rare earth—transition metal phase diagram. The location of the Fermi level relative to the top of the 3d-band has been estimated using the magnetic properties of these materials, and a strong correlation has been found between its position and the existence of a particular compound. Specifically the A3B and AB phases exist only for Ef above the 3d states, while the A4B3 and possibly the AB2 structure require the Fermi level to intersect the 3d-band. Es wird der Versuch unternommen, die Existenz der kristallographischen Phasen zu erklaren, die in dem Seltenen Erden—Ubergangsmetall-Phasendiagramm beobachtet werden. Die Lage des Ferminiveaus bezuglich der oberen Kante des 3d-Bandes wird mit den magnetischen Eigenschaften dieser Materialien berechnet und eine starke Korrelation zwischen seiner Lage und der Existenz einer speziellen Verbindung gefunden. Insbesondere existieren die A3B- und AB-Phasen nur fur Ef oberhalb der 3d-Zustande, wahrend die A4B3 und moglicherweise die AB2-Strukturen fordern, das das Ferminiveau das 3d-Band schneidet.

The effects produced by the simultaneous application of more than one type of stimulus to phosphor materials are reviewed. The observed phenomena induced by the presence of an electric field during stimulation are discussed. It was found that in general when a steady, alternating, or pulsed electric field is applied to a phosphor in the form of a powder, film, or single crystal, excited with ultraviolet light, x rays, cathode rays, or alpha particles, a quenching of the emitted light occurs. However, for some conditions such as manganese activation and chlorine coactivation, an increase in the luminescence intensity can be induced by the field. It is possible for both enhancement and quenching to be observed in a single specimen and for the spectral dependence of the effects to change with field frequency, illumination intensity, and temperature. Fieldinduced processes in ZnS and CdS phosphors are described. Theoretical explanations are presented. (M.C.G.)