Toshio Kosugi

A New Low-Temperature Dislocation-Relaxation Peak in Aluminum

Amplitude-independent internal friction measurement is made on a zone-refined aluminum single crystal between 2–240 K by a composite oscillator method. In the lightly deformed state \(({\lesssim}10^{-4})\), a new relaxation peak is clearly found at 11 K. The activation energy of this peak is derived to be about 0.01 eV by assuming the attack frequency f 0 =10 10 s -1 , and if the peak is due to the kink pair formation of the dislocation on the Peierls potential valley, the Peierls stress is estimated to be about 10 -5 µ (µ: shear modulus), which does not conflict with the yield stress of low-temperature plastic deformation measurements.

Thermal conductivity of GeO2SiO2 and TiO2SiO2 mixed glasses

Abstract The thermal conductivities of binary mixed glasses, GeO 2 SiO 2 and TiO 2 SiO 2 , have been measured. Two GeO 2 SiO 2 glasses measured are composed of 5 and 10 mol% of GeO 2 , and the one TiO 2 SiO 2 glass which was measured is composed of 5.7 mol% of TiO 2 . At temperatures below 1 K, the thermal conductivities of both types of mixed glasses have a T 1.8 dependence on temperature. The magnitude of the thermal conductivity of GeO 2 SiO 2 increases with increasing GeO 2 concentration. The thermal conductivity of TiO 2 SiO 2 is higher than that of pure SiO 2 at temperatures above 10 K but is smaller at lower temperatures. At temperature between a few K to about 20 K, the thermal conductivities of GeO 2 SiO 2 glasses have a typical plateau while that of the TiO 2 SiO 2 glass has a ‘shoulder’.

A new internal friction peak and the problem of the Peierls potential in f.c.c. metals

Abstract A new internal friction peak has been discovered at 11 K for 53 kHz in a high purity aluminum crystal which had been lightly deformed at room temperature. It can be explained satisfactorily by the kink pair formation mechanism of dislocations. As a result, the Peierls stress τ p in an f.c.c. metal has been derived quantitatively for the first time, i.e. τ p ≈ 3×10 −5 μ (μ is the shear modulus), which is small compared with measured plastic properties. Phenomena related to the dislocation configuration and dynamics such as the limitation of the string model approximation and the influence of the Peierls potential in f.c.c. metals are discussed in the light of these new results.

Problem of Acoustic Absorption Measurement by Composite Oscillator Method: Low-Temperature Internal Friction Peaks in Quartz

It is demonstrated that accurate measurements of internal friction can be made by a two-component composite oscillator method (COM), which was first proposed by Schwarz [Rev. Sci. Instrum. 48 (1977) 111]. The problems concerning COM are also discussed; in particular, the influence of the internal friction peaks in quartz used as a piezoelectric transducer is discussed for the first time.

Ultrasonic study of the interaction potential between a dislocation and a single solute atom

Abstract The interaction potential between a dislocation and a single solute atom was investigated using the amplitude-dependent internal friction (ADIF) at 1.6–30 K in pure Al crystals, into which were introduced a single kind of solute atom, i.e. 100 ppm Zn, 50 ppm Ag, 25 ppm Mg and 20 ppm Cu respectively. The following common features were found for all crystals for the temperature dependence of the applied stress amplitude σ0 under constant ADIF. (1) At lower temperatures, σ0 changes linearly with T 2 3 . The T 2 3 law holds at σ 0 σ 0 (T=0) ⪆ 0.65 , where σ0 (T=0) is the extrapolated value of the T 2 3 dependence. (2) A simple potential, where the Cottrell type potential based on the linear elastic theory is modified to become flat near the dislocation center, can explain the temperature dependence of σ0 satisfactorily except at σ 0 σ 0 (T=0)⪆0.87 . These results mean that the shape of the interaction potential is the same for all the solutes and the real interaction potential becomes shallower near the dislocation center than is expected from the solution derived using the linear elastic theory. The interaction energies of a dislocation and a single solute atom were determined as 0.11, 0.135, 0.19 and 0.195 eV for Zn, Ag, Mg and Cu respectively.

Ultrasonic attenuation in glasses of SiO2GeO2 mixture

Ultrasonic absorption on SiO2-5 mole% GeO2 and SiO2-10 mole% GeO2 glasses between 1.6–250 K shows that the most probable origin of the structural relaxation of SiO2 glass is the transverse motion of the oxygen atom in SiOSi bridge among existing models. In addition it is also suggested that the same structure is the origin of two-level system (TLS) phenomena below 10 K.

Internal friction measurement of organic glass below and near the glass transition temperature

Abstract Internal friction (IF) measurements were made over a wide frequency range, 0.001–10 Hz, for temperatures in the range 11–74 °C. A forced vibration method was adopted using the Vibran apparatus. The specimens used were from the typical organic glass polystyrene, and the measurements were performed on the glassy state from room temperature up to a temperature close to the glass transition. A viscous type relaxation, IF inversely proportional to frequency, was observed at all temperatures. The relaxation time was determined as a function of temperature at various frequencies. The relaxation behavior showed a double relaxation: a combination of two thermal-activation type relaxations. This result was quite similar, especially at lower frequencies, to the result derived from the static viscosity measurement for the same material

Experimental Determination of the Force-Distance Relation for the Interaction between a Dislocation and a Solute Atom

In order to obtain the information on the force-distance relation for the interaction between a dislocation and a solute atom, the amplitude-dependent internal friction was measured at 1.7-30 K on Al-100 at ppm Zn and Al-50 at ppm Zn single crystals.The temperature dependence of the applied strain under a constant decrement was exactly the same for the two crystals. The data were analized by using the thermally assisted break-away theory for pinned dislocations with assttming several forms of the interaction potential. A modified Cottrell potential was considered, in which the interaction force was cut off at a critical distance close to the center of dislocation. This model was found to be able to explain the temperature dependence of the applied strain satisfactorily, and the critical distance was estimated to be 1.4 A.

Internal friction of SiO2 glasses with excessive and deficient oxygen

The lack of stoichiometry in SiO2 glass causes optical absorption, luminescence and so on. The internal friction of SiO2 glasses with excessive and deficient oxygen was measured in the temperature range of 1.6–250 K. At 35 K excessive oxygen enhanced the intensity of the internal friction of the glass, and deficient oxygen reduced this intensity. These changes of internal friction are analyzed by the bending model related to bridging oxygens in SiOSi bonds. Densitues of both the excessive and deficient oxygen are in the order of 1017/cm3. It is supposed tha the changes in Youngs modulus of these glasses are due to the OH contents.

Distribution of double-well potentials in SiO2 and SiO2: Ge glasses

Abstract The temperature dependence of the internal friction and the elastic modulus of pure SiO 2 and SiO 2 : Ge glasses measured by 50 kHz composite oscillator method have been analyzed on the basis of the double-well potential model. The density of relaxation strength and the distribution of the asymmetry parameter have been determined uniquely for pure SiO 2 , SiO 2 5% GeO 2 , and SiO 2 10%GeO 2 specimens by fitting the asymmetry potential model to the internal friction and elastic modulus data. The asymmetry parameter is found to increase with the doping of Ge atoms.