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Infrared active modes in KTaO3
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ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS ANNEALING OF GOLD AFTER MODERATELY, FAST HEATING R. 0. Simmons (Materials Research Laboratory and Department of Physics, University of illinois, Urbana, illinois, U. S. A.) and R. W. Balluffi (Materials Research Laboratory and Department of Mining, Metallurgy, and Petroleum Engineering, University of Illinois, Urbana, Illinois, U.S.A.).
~strom has reported significant heat absorption in high purity silver, gold, aluminum, and molybdenum and expansion in gold during Isothermal annealing immediately following heating from room temperature to temperatures, T , in the range 433 to 753°K at rates 50 to lT6~OoKmind. The relative linear isothermal expansion in gold was claimed to be AL/L~--(1.7K 10-3) exp [(- 0.26 * 0.08) eV/kTm] exp(-t/r), where i was 2 to 3 hr, similar to the time constant given by the calorimetric work. These results are experimentally inconsistent with the production of thermal vacancies or other currently recognized lattice defects or with the dissolution of precipitates; they were therefore tentatively explained in terms of the “structural defects” having similar activation energies postulated in the phenomenological analyses of Borelius. In the present work attempts were made to verify the existence of “structural expansion” under conditions similar to those of Astroni by measuring changes in the, x-ray lattice constant, ta/a, during the isothermal annealing or gold after moderately fast heating. For structural defects producing lattice dilatations, Aa/a = AL/L. Two rapid x-ray techniques were used on 99. 999 per cent gold crystal at Tm = 752 and 850°Kfor which the equation above predicts total expansions of 32 ppm and 50 ppm, respectively. No detectable trace (~4ppm) of the claimed expansion was found, and it was concludid that there was no basis to support either Astrom’s experiments or their interpretation. (Received 20 April 1964) 16.
THEORY OF SPECIFIC HEATS OF DILUTE ALLOYS A. D. Boardman (Dept. of Pure and
Vol. 2, No. 6
Applied Physics, Royal College of Advanced Technology, SaJ.ford, England) and N. H. March (Dept. of Physics, The University, Sheffield, England). Two results which appear to have relevance in the interpretation of specific heats of dilute alloys are derived. The first concerns the density of states at the Fermi level, calculated using Blodi waves in the unperturbed matrix, and treating the impurity potential to first order. The result is exact in band theory to this order. Secondly, it is pointed out that the temperaturedependent self-consistent perturbing potential should be used in the evaluation of the alloy specific heat. The magnitude of the effect is calculated for plane waves, and multiplies the usual first order result by a factor of 4/3. The effect of band structure and temperature together will evidently have to be estimated before detailed comparison with experiment can be made, but this necessitates accurate knowledge of the Dirac density matrix for the pure metal and this information is not at present available. (Received 23 April 1964) -
17.
INFRARED ACTWE MODES IN KTaO3 R. I. Joseph and B. D. Silverman (Raytheon Research Division, Waltham, Massachusetts, U. S. A.).
With neglect of all but the three largest restoring couplings between the sublattices of KTaO3, the three observed optical frequencies enable one to calculate the displacements associated with each normal mode. As in the case of SrTiO3, one again obtains a Slater-type low-frequency solution. The low and intermediate frequencies are characterized by a relatively rigid oxygen framework. The high frequency involves large relative motion of the oxygen ions. In the case of KTaO3, a Lasttype solution does not exist over an extended temperature range. The displacements associated with the corresponding three modes of the Slater-type solution for SrTiO3 and KTaO3 are similar, which is what one might expect due to the similarity of the reflectivity spectra of these materials. (Received 11 May 1964)
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS ANNEALING OF GOLD AFTER MODERATELY, FAST HEATING R. 0. Simmons (Materials Research Laboratory and Department of Physics, University of illinois, Urbana, illinois, U. S. A.) and R. W. Balluffi (Materials Research Laboratory and Department of Mining, Metallurgy, and Petroleum Engineering, University of Illinois, Urbana, Illinois, U.S.A.).
~strom has reported significant heat absorption in high purity silver, gold, aluminum, and molybdenum and expansion in gold during Isothermal annealing immediately following heating from room temperature to temperatures, T , in the range 433 to 753°K at rates 50 to lT6~OoKmind. The relative linear isothermal expansion in gold was claimed to be AL/L~--(1.7K 10-3) exp [(- 0.26 * 0.08) eV/kTm] exp(-t/r), where i was 2 to 3 hr, similar to the time constant given by the calorimetric work. These results are experimentally inconsistent with the production of thermal vacancies or other currently recognized lattice defects or with the dissolution of precipitates; they were therefore tentatively explained in terms of the “structural defects” having similar activation energies postulated in the phenomenological analyses of Borelius. In the present work attempts were made to verify the existence of “structural expansion” under conditions similar to those of Astroni by measuring changes in the, x-ray lattice constant, ta/a, during the isothermal annealing or gold after moderately fast heating. For structural defects producing lattice dilatations, Aa/a = AL/L. Two rapid x-ray techniques were used on 99. 999 per cent gold crystal at Tm = 752 and 850°Kfor which the equation above predicts total expansions of 32 ppm and 50 ppm, respectively. No detectable trace (~4ppm) of the claimed expansion was found, and it was concludid that there was no basis to support either Astrom’s experiments or their interpretation. (Received 20 April 1964) 16.
THEORY OF SPECIFIC HEATS OF DILUTE ALLOYS A. D. Boardman (Dept. of Pure and
Vol. 2, No. 6
Applied Physics, Royal College of Advanced Technology, SaJ.ford, England) and N. H. March (Dept. of Physics, The University, Sheffield, England). Two results which appear to have relevance in the interpretation of specific heats of dilute alloys are derived. The first concerns the density of states at the Fermi level, calculated using Blodi waves in the unperturbed matrix, and treating the impurity potential to first order. The result is exact in band theory to this order. Secondly, it is pointed out that the temperaturedependent self-consistent perturbing potential should be used in the evaluation of the alloy specific heat. The magnitude of the effect is calculated for plane waves, and multiplies the usual first order result by a factor of 4/3. The effect of band structure and temperature together will evidently have to be estimated before detailed comparison with experiment can be made, but this necessitates accurate knowledge of the Dirac density matrix for the pure metal and this information is not at present available. (Received 23 April 1964) -
17.
INFRARED ACTWE MODES IN KTaO3 R. I. Joseph and B. D. Silverman (Raytheon Research Division, Waltham, Massachusetts, U. S. A.).
With neglect of all but the three largest restoring couplings between the sublattices of KTaO3, the three observed optical frequencies enable one to calculate the displacements associated with each normal mode. As in the case of SrTiO3, one again obtains a Slater-type low-frequency solution. The low and intermediate frequencies are characterized by a relatively rigid oxygen framework. The high frequency involves large relative motion of the oxygen ions. In the case of KTaO3, a Lasttype solution does not exist over an extended temperature range. The displacements associated with the corresponding three modes of the Slater-type solution for SrTiO3 and KTaO3 are similar, which is what one might expect due to the similarity of the reflectivity spectra of these materials. (Received 11 May 1964)