A. C. Ehrlich

The effect of rare‐earth filling on the lattice thermal conductivity of skutterudites

Polycrystalline samples of Ir4LaGe3Sb9, Ir4NdGe3Sb9, and Ir4SmGe3Sb9 have been made by hot isostatic pressing of powders. The lattice thermal conductivity of these filled skutterudites is markedly smaller than that of IrSb3; thus, void filling shows promise as a method for improving the thermoelectric properties of these materials. We present the lattice thermal conductivity of these filled skutterudites in an effort to quantify the impact of void filling in this structure. It is believed that the atoms ‘‘rattle’’ in the voids of the structure and therefore interact with a broad spectrum of lattice phonons, reducing their mean free paths substantially below that in the ‘‘unfilled’’ skutterudites. An additional phonon scattering mechanism is caused by phonon‐stimulated transitions between the low‐lying energy levels of the 4f electron configurations in the case of Nd3+ and Sm3+. Magnetic susceptibility and Hall‐effect measurements are also presented.

A study of rf nonlinearities in nickel

A new and very sensitive method (1 part in 1019) for studying nonlinear properties of metallic systems under the influence of radio-frequency fields is described. The method is applied to a study of the intermodulation generation at 150 MHz in nickel as a function of a dc field and as a function of the power of the two simultaneously applied rf fields at 146 and 148 MHz. As the dc field is increased for a given applied rf power, the intermodulation signal shows a number of linear regions of decrease on a semilogarithmic graph. Different results are obtained which depend on the relative orientations of the dc and rf magnetic fields. The power of the intermodulation signal shows a cubic or quadratic dependence on the power of the applied rf fields for low or high values of the dc field, respectively. These results are discussed in terms of the interaction of the rf field with the domain walls using a recent model of an electroplated nickel domain structure proposed by others.

Device for simultaneously measuring stress, strain, and resistance in ‘‘whiskerlike’’ materials in the temperature range 1.5 K<T<360 K

We describe a device for measuring Young’s modulus Y and the piezoresistance of ‘‘whiskerlike’’ samples. The device can be used in a standard vari‐temp Dewar in the temperature range 1.5 K<T<360 K. One end of the sample is attached to a movable rod suspended by leaf springs and the other end is held fixed. Force is applied to the rod by a coaxial electromagnet acting on permanent magnets attached to the rod. Displacements are measured with a capacitive technique. We have used the device to measure Young’s modulus for the charge density wave material TaS3. We also measured the Young’s modulus of some Cu whiskers for comparison.

Response of piezoelectric bimorphs as a function of temperature

The temperature dependence of the response of piezoelectric ‘‘bimorphs’’ ■ (■ Registered trademark of Vernitron Corp., Bedford, OH) has been studied. This response is markedly decreased as temperature is decreased. Since the bimorphs are voltage limited, the amount of motion available is thus reduced as the temperature is lowered. This effect is important in the design specifications for the use of bimorphs at low temperatures.

Anisotropy effects in the linearly polarized x-ray absorption spectrum of Br2 intercalated graphite fibers and highly oriented pyrolytic graphite

Abstract Angle dependent Br K edge x-ray absorption spectra were obtained for residual compounds of Br 2 intercalated HOPG and TP4104B graphite fibers using polarized synchrotron radiation. In both materials, the bromine appears to be in the form of Br 2 molecules oriented at an angle of about 20° with respect to the graphite planes. The intramolecular distance is found to be 2.31A. Br-C EXAFS has also been observed and indicates that the Br 2 molecules lie between the graphite planes.

Influence of Size Effect on Low‐Temperature Electrical Resistivity

The low‐temperature electrical resistivity in thin plates has been theoretically examined. It is shown that the bulk relaxation time τi is a reasonable approximation to describe the impurity scattering. In constrast, the low‐temperature phonon‐electron interaction is not properly described by the bulk thermal relaxation time τp. Nevertheless, expressions have been obtained for the Fermi function in thin plates correct to first order in τi/τp≪1. The predicted temperature‐dependent resistivity obtained is smaller than the results predicted by Fuchs, which are also given explicitly in this limit for the first time. In the limit of very low temperatures and very thin plates a temperature dependence of resistivity greater than the bulk value, but ⅔ that obtained by Fuchs, is predicted. These results are discussed.

A Search for Anomalies in the Palladium-Deuterium System

A polycrystalline palladium rod is electrolytically charged with deuterium up to a deuterium/palladium ratio of 0.81 while several sample parameters are simultaneously measured in situ, including electrical resistivity, sample dimensions, cell temperature, and neutron production. Various charging rates are used in an attempt to provoke any anomalous behavior, such as a previously unknown crystallographic or chemical phase change, that might account for reports of heat or neutron production. Neither the electrical resistivity nor sample dimensions manifest evidence of any anomaly.

Properties of graphitized carbon fiber-halogen residue compounds

Abstract Br2 or ICl residue compound formation in TP 4104B and GY-70 fibers increases their electrical conductivity 3–5 times. It also decreases the tensile strength of the GY-70 fibers by increasing their cross-sectional area. In contrast, the tensile strength of the TP 4104B fiber remains unchanged on Br2 or ICl residue compound formation. The TP 4104B/Br2 residue compound loses only 1–2% of its weight and increases its resistance by only 5–10% when heated to 400°C in air; the ICl residue compounds of both fibers are unstable above 150°C. The temperature coefficient of resistivity of the unintercalated fibers (in the range 2–673 K) is attributed to a temperature dependent variation in the number of current carriers in the intercrystalline regions of the fibers and not to a finite resistance percolation path through the graphite crystallites. The magnetoresistance of the fibers from 2–200 K is attributed to a large resistance increase within the graphite crystallites. Both the temperature coefficient of resistivity and the magnetoresistance of the residue compounds are consistent with a metallic-like electron structure. The preparation of bromine residue compounds of individual TP 4104B fibers that had different bromine concentrations was not successful; fibers either intercalated Br2 and formed the “full” residue compound or remained unintercalated.

Quantum size effect and the giant magnetoresistance in magnetic multilayers

A theoretical model which accounts for the variations of the giant magnetoresistance, Δρ/ρ, with electron mean free path, L, interface roughness, r, and magnetic, tM, and normal layer, tN, thickness has been previously presented for sandwich films. It employs the quantum‐size‐effect theory of resistivity in thin films and relies on spin dependent transmission or reflection at individual layer boundaries to establish the metallic quantum‐well states. This model has now been extended (i) to films where L can be different in the magnetic, LM, and nonmagnetic, LN, layers, (ii) to an electron/atom number, n, of 0.131 as well as 1.047, and (iii) to films from sandwiches to those with as many as 64 (63) magnetic (nonmagnetic) layers. The focus is on films with relatively thin tM and tN where quantum, as distinguished from semiclassical, effects should dominate. Typical results can be summarized as follows: for tM∼tN∼10 monolayers, ML, and L’s∼70 ML, Δρ/ρ increases more rapidly as LM than LN, but this effect is r...

Temperature-dependent magnetoresistance of Fe-Ni multilayers

Temperature‐dependent longitudinal and transverse magnetoresistance measurements have been carried out on a series of five Fe‐Ni multilayer thin films. The samples were prepared by sputtering onto glass substrates that were nominally at room temperature and proved to be highly textured with the (111) direction perpendicular to the substrate. The multilayer wavelength ranged from 21 to 155 A with each sublayer composed of an equal number of monolayers of Fe and Ni. For the larger‐wavelength films the magnetoresistance data shows a preferred direction of in‐plane magnetization associated with the film growth parameters. With the field perpendicular to the plane the data shows the characteristic break at the applied magnetic field required for saturation. This saturation field is not temperature dependent and does not vary much or in any systematic manner with wavelength. Above the saturation field the magnetoresistance varies linearly with applied field with a slope, dR/dH, that varies systematically with t...