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Dislocation behavior during anelastic strain recovery in zinc single crystals prestrained under basal glide
ii 4.
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS DISLOCATION BEHAVIOR DURING ANELASTIC STRAIN RECOVERY IN ZINC SINGLE CRYSTALS PRESTRAINED UNDER BASAL GLIDE N. Mikuriya, Department of Physics, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan; and M. Okochi, Department of Physics, Faculty of Science and Engineering, Meijo University, Yagoto, Tenpaku-ku, Nagoya 468, Japan.
Anelastic strain recovery experiments on zinc single crystals strained under basal glide were performed as a function of the forest pyramidal dislocation density at room temperature. The instantaneous strain recovery of specimens unloaded after prestraining in compression is proportional to 17~"s where l is the average spacing between forest dislocations and 7p is the prestrain. It is suggested that the instantaneous strain recovery results from the back motion of basal dislocations which multiplied under prestraining. The basal dislocations move to back under the influence of the internal stress unless they are impeded by intersection with fores dislocations. The time dependent strain recovery was measured on all specimens in either the unloaded or partially unloaded states, which enabled the activation volume of the process to be determined. The time dependent strain recovery is explainable in terms of the thermally activated back motion of basal dislocations via cutting the forest dislocations. Received 2 December 1981 Revised 3 March 1982
5.
CALORIMETRIC STUDY OF PROTON ORDERING IN HEXAGONAL ICE CATALYZED BY HYDROGEN FLUORIDE Masakatsu Ueda, Takasuke Matsuo and Hiroshi Suga, Department of Chemistry and Chemical Thermodynamics Laboratory, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan.
Heat capacities of hexagonal ices doped with 2.6, 26 and 260m mol dm -3 HF were measured with an adiabatic calorimeter. The HF doping accelerated proton ordering which has been known to take place sluggishly around 100 K. The ice containing 26 m mol dm -3 HF showed the largest excess entropy [(0.102 -+ 0.01) J K -1 mol -I ] and the shortest relaxation time. The relaxation time at 90K was about 1/30 of that of the pure ice I h at the same temperature. The activation enthalpies obtained were the same for all of the doped ices, (23.5 + 2.0) J mol-t, which is approximately equal to the activation energy of the mobility of the Bjerrum L-defect.
Vol. 44, No. 9
Received 30 November 1981 Revised 3 March 1982
6.
MAGNETIC AND STRUCTURAL CHARACTERISTICS OF THE RaNiTB2 COMPOUNDS (R = RARE EARTH) Israel Felner, Racah Institute of Physics, The Hebrew University, Jerusalem, Israel
Magnetic and structural behaviour and phase relationships of materials of composition R aNi7B2 (R = Nd-Lu) were investigated. Detailed X-ray analysis yields that two hexagonal structures are encountered. For the heavy rare earth (Gd-Lu) the compounds crystallize in the CeNia structure. The space group is P63/mmc and each unit cell contains two formula units. The R3NiTB: where R = Nd-Sm (including Yb3NiTB2) crystallize in the CeCo4B structure. The space group is P6[mmm and each unit cell contains one formula unit. The detailed crystal structures are discussed. The magnetic measurements show that Yb3NiTB2 and LuaNiTB2 are Pauli paramagnetic. SmaNiTB 2 is ferromagnetically odered with a huge intrinsic magnetic hardness. The magnetization at the coercise field at low temperatures is extremely time dependent. The R3NiTB2 which crystallize in CeNi3 structure are antiferromagnetic at low temperature. All M6ssbauer and magnetization experimental results can be explained assuming an antiferromagnetic exchange interaction in both 2(c) and 4 ( f ) crystallographic sites and a ferromagnetic interaction between these sites. Received 24 November 1981
7.
POSITRON ANNIHILATION IN Pb 2+ DOPED KC1 SINGLE CRYSTALS M. Chinnusamy, S. Ramasamy, T. Nagarajan and V. Manohar, Department of Nuclear Physics, University of Madras, A.C. College Campus, Madras 600 025, India.
The angular distribution of annihilation photons (ADAP) has been measured in a pure KC1 single crystal and in one doped with Pb 2+ impurities to concentrations of 100, 550 and 1050ppm. In unannealed, impurity doped, crystals the intensity of the narrow component increases with increase of impurity concentration. The narrowing of the ADAP curves is explained by assuming trapping of positrons at impurity induced positive ion vacancies. On annealing, the result on the 550 ppm impurity doped crystal shows that there is a dissolution of impurity-vacancy complexes at nominal concentrations of impurity, and the result on the 1050 ppm crystal shows that there is precipitation of impurity for very high concentrations.
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS DISLOCATION BEHAVIOR DURING ANELASTIC STRAIN RECOVERY IN ZINC SINGLE CRYSTALS PRESTRAINED UNDER BASAL GLIDE N. Mikuriya, Department of Physics, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan; and M. Okochi, Department of Physics, Faculty of Science and Engineering, Meijo University, Yagoto, Tenpaku-ku, Nagoya 468, Japan.
Anelastic strain recovery experiments on zinc single crystals strained under basal glide were performed as a function of the forest pyramidal dislocation density at room temperature. The instantaneous strain recovery of specimens unloaded after prestraining in compression is proportional to 17~"s where l is the average spacing between forest dislocations and 7p is the prestrain. It is suggested that the instantaneous strain recovery results from the back motion of basal dislocations which multiplied under prestraining. The basal dislocations move to back under the influence of the internal stress unless they are impeded by intersection with fores dislocations. The time dependent strain recovery was measured on all specimens in either the unloaded or partially unloaded states, which enabled the activation volume of the process to be determined. The time dependent strain recovery is explainable in terms of the thermally activated back motion of basal dislocations via cutting the forest dislocations. Received 2 December 1981 Revised 3 March 1982
5.
CALORIMETRIC STUDY OF PROTON ORDERING IN HEXAGONAL ICE CATALYZED BY HYDROGEN FLUORIDE Masakatsu Ueda, Takasuke Matsuo and Hiroshi Suga, Department of Chemistry and Chemical Thermodynamics Laboratory, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan.
Heat capacities of hexagonal ices doped with 2.6, 26 and 260m mol dm -3 HF were measured with an adiabatic calorimeter. The HF doping accelerated proton ordering which has been known to take place sluggishly around 100 K. The ice containing 26 m mol dm -3 HF showed the largest excess entropy [(0.102 -+ 0.01) J K -1 mol -I ] and the shortest relaxation time. The relaxation time at 90K was about 1/30 of that of the pure ice I h at the same temperature. The activation enthalpies obtained were the same for all of the doped ices, (23.5 + 2.0) J mol-t, which is approximately equal to the activation energy of the mobility of the Bjerrum L-defect.
Vol. 44, No. 9
Received 30 November 1981 Revised 3 March 1982
6.
MAGNETIC AND STRUCTURAL CHARACTERISTICS OF THE RaNiTB2 COMPOUNDS (R = RARE EARTH) Israel Felner, Racah Institute of Physics, The Hebrew University, Jerusalem, Israel
Magnetic and structural behaviour and phase relationships of materials of composition R aNi7B2 (R = Nd-Lu) were investigated. Detailed X-ray analysis yields that two hexagonal structures are encountered. For the heavy rare earth (Gd-Lu) the compounds crystallize in the CeNia structure. The space group is P63/mmc and each unit cell contains two formula units. The R3NiTB: where R = Nd-Sm (including Yb3NiTB2) crystallize in the CeCo4B structure. The space group is P6[mmm and each unit cell contains one formula unit. The detailed crystal structures are discussed. The magnetic measurements show that Yb3NiTB2 and LuaNiTB2 are Pauli paramagnetic. SmaNiTB 2 is ferromagnetically odered with a huge intrinsic magnetic hardness. The magnetization at the coercise field at low temperatures is extremely time dependent. The R3NiTB2 which crystallize in CeNi3 structure are antiferromagnetic at low temperature. All M6ssbauer and magnetization experimental results can be explained assuming an antiferromagnetic exchange interaction in both 2(c) and 4 ( f ) crystallographic sites and a ferromagnetic interaction between these sites. Received 24 November 1981
7.
POSITRON ANNIHILATION IN Pb 2+ DOPED KC1 SINGLE CRYSTALS M. Chinnusamy, S. Ramasamy, T. Nagarajan and V. Manohar, Department of Nuclear Physics, University of Madras, A.C. College Campus, Madras 600 025, India.
The angular distribution of annihilation photons (ADAP) has been measured in a pure KC1 single crystal and in one doped with Pb 2+ impurities to concentrations of 100, 550 and 1050ppm. In unannealed, impurity doped, crystals the intensity of the narrow component increases with increase of impurity concentration. The narrowing of the ADAP curves is explained by assuming trapping of positrons at impurity induced positive ion vacancies. On annealing, the result on the 550 ppm impurity doped crystal shows that there is a dissolution of impurity-vacancy complexes at nominal concentrations of impurity, and the result on the 1050 ppm crystal shows that there is precipitation of impurity for very high concentrations.