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The magnetic behaviour of diluted CrAl alloys
Vol. 40, No. 5
ABSTRACTS
OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
with the evident distrrbutions between the prmcipal g values arising from an isotropic randomness at the titamum sites. However, the g parameter drstributrons of the hole resonance, and theu changes during the addition of TiOz indicate the development of Silicate structures in the glasses which are the precursors of the major low temperature crystalline phases The invanance of the hole and electron resonance lmes with pre-crystallrzatron heat treatments indicates that neither the titanium associated structures of the basic silicate structure of the glass are changed by such treatments. Recewed 23 December 1980 Revised 20 March 198 1 9
THE HOPPING MOTION OF THE SELFTRAPPED EXCITON IN NaCl
was investigated wrth X-rays. The sample used in the experrment showed a macroscopic hydrogen density mode, leading to a curvature of the whole crystal plate wrth the o-phase on the concave side and the cy’-phase on the convex side. In addition an o-phase wettmg layer was found on top of the or-phase separated from the bulk cur-phase by a mrxed (Y-Q’ phase regron. In a snnple model therr thickness was determmed to about - 1 0 and - 7.0 m, resp. This thm wetting layer leads to a new interpretation of the phase transitron of H and Nb, mvolvmg the fanuliar long-range elastic mteractron as well as a short-range surface free energy contrrbutron. Recerved 15 December 1980
11.
K. Tammura and N. Itoh, Department of Crystallme Materials Science, Faculty of Engmeermg, Nagoya University, Nagoya 464, Japan. The decay kmetrcs and the yield of the n luminescence from the lowest triplet state of the self-trapped exciton have been studied m NaCl contammg Lr+ ions. It 1s found that the n lummescence band which 1s observed at 6 K 1s replaced by a lummescence band peaked at 3.34 eV above 77 K. The 3.34 eV lummescence band is ascribed to the recombmatron of the relaxed excrton trapped by a Lr+ ion, (V,e),. The decay of the n lummescence induced by an electron pulse and the time change of the lummescence from are explamed in terms of the characterrstrc (vke)Ll equation of the diffusron-limited reaction of the lowest tripled self-trapped excrtons with the Li+ ions. From the analysis of the dependence of the decay rate of the 7r lummescence on temperature and on the Lt+ concentration, we found the drffusron constant D of the lowest tnpled self-trapped exciton in NaCl to be grven by D = D,,e-Ea’kT withD, = 2.13 x 10s3 cm* see-’ and E, = 0.13 eV. The present result can be regarded as the first clear experrmental evidence for the hoppmg drffusion of the self-trapped exciton in alkali halides. The obtamed values of E, and Do are discussed usmg the small polaron theory. The effect of the anharmomcrty on the hoppmg of the self-trapped excrtons 1s suggested to be srgnificant. Received 29 December 1980 10.
CRITICAL POINT WETTING IN NbH,.B, H. Zabel, B. Schonfeld and S.C. Moss, Physics Department, University of Houston, Houston, TX 77004, U.S.A.
The local o--o phase distrtbutron 111a thm Nb smgle crystal loaded with the crrtrcal H-concentratron
ui
THE SOLID STATE REACTION BETWEEN AgI AND Hg12 V Leute and B. Schroder, Institute of Physrcal Chemistry, University of Munster, Schlossplatz 4,440O Munster, Germany.
The kmetrcs of the solid state reaction between AgI and Hg12 1s mvestrgated experimentally by measurmg the thickness of the layer of the oz-Ag2Hg14 product phase as a function of the annealing tune and the reaction temperature. A theoretical expression 1s denved whrch allows the calculatron of the variation of the chemical potentials of the binary components across the product layer consrdermg the vanatron of the product phase composition A value of A0 = 6 KJ mole-’ 1s estimated for the standard affinity for the formation of storchrometrrc Ag, Hg14 from the binary components AgI and Hg12. Recewed 19 December 1980 Revised 20 March 198 1
12.
THE MAGNETIC BEI-IAVIOUR OF DILUTED CrAl ALLOYS I Pop, D. Dadlrlat, T. Petrrsor and A. Gmrgm, Department of Physrcs, Cluj-Napoca University, 3400 CluJ-Napoca, Romania
Magnetic susceptrbrhty as a function of temperature of binary CrAl alloys contammg 0.7, 1.07, 1 35, 1.59, 1.79, 1.98,2.18, 2.84,3.74 and 4.36 at.% Al 1s mvestigated. Alummmm, by alloymg, acts on the Neel temperature of pure chrommm gwmg rrse to a complicated phase diagram The behavrour of the magnetic susceptrbility as a function of temperature, m the ordered phase, for the samples contammg 1 28,2.18 and 2.84 at.% Al 1s found to be temperature independent. In the paramagnetrc region, for the samples contaimng between 1.07
iv
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
and 2.84 at.% Al, it is found a decrease of the magnetic susceptibility as a functron of temperature. Recerved 23 September 1980 Revised 29 March 198 1 13.
ELECTRON TRANSPORT IN SEMICONDUCTORS IN THE PRESENCE OF IMPACT IONIZATION A. Reklaitrs, Semiconductor Physrcs Institute of the Academy of Sciences of the Lithuanian SSR, Vilmus, USSR
The development of impact ionization m semiconductors has been consrdered. A transport equation for the electron drstrrbutron function m the presence of impact ronization has been derived. It has been found that the collisron integral of this equation 1s nonlinear with respect to the distribution function The relatron between the solutions of this equatron and the usual Boltzmann equation have been determmed. A Monte Carlo method for numerical calculations m the presence of impact romzation has been developed. The results of numerical calculations carrred out usmg a srmphfied model of mdmm antimomde are presented Recerved 28 Ju& 1980 Revised 29 March 1981 14.
CORRELATION BETWEEN DEFECT STRUCTURES AND DIELECTRIC CONSTANT IN GALLIA-DOPED RUTILE (TiOZ) E. Iguchr, K, Ogmo and H. Sawatari, Department of Metallurgical Engmeermg, Faculty of Engmeermg, Yokohama Natronal Umversity, Tokiwadai, Hodogaya-Ku, Yokahama, 240 Japan, and R.J .D Tllley , School of Materials Science, Umversrty of Bradford, Bradford, BD7 lDP, West Yorkshire, England
Drelectrrc constants and a.c. resntrvmes of rutrle (TrO,) doped with galha (Ga, 0,) have been measured as a function of frequency m the range 30-60 kHz at 20” C. The specrmens were prepared by heating rutile smgle crystals on Gaz 0s pellets, at 1300’ C, in air for various times. The dielectric constants depend on the frequency of measurement. In the c axis, the drelectric constant at low frequencies (30-100 Hz) mcreases as the sample heating tune is extended to 1 week, but rt decreases raptdly when the heating time 1s prolonged over 1 week. However, m the a axis, the dielectric constant does not change from the value of the starting materral, being independent of the heatmg trme. Besides drelectnc measurements, the defect structures were determmed using transmissron electron mrcroscopy, which showed that low concentrations of planar faults
Vol. 40, No. 5
on (120) planes occur. The changes m dielectric constant are mterpreted as bemg due to space charge effects associated with Ga3+ ions located in the tunnels which he parallel to the rutrle c axis. Calculatrons are also mcluded which show why other defects m the crystals have no effect on the value of the dielectric constant compared to pure r-utile. Received 17 December 1980 Revised 3 1 March 198 1 15.
DIFFUSION AND NMR SPIN LATTICE RELAXATION OF ‘H IN 0~’TaH, AND NbHZ F.E. Mauger, W.D. Wrlhams and R.M. Cotts, Laboratory of Atomic and Sohd State Physrcs, Cornell University, Ithaca, NY 14853, U.S A
The concentratron and temperature dependence of the self diffusion coefficient, D, of H m Group V transrtron metals Nb and Ta has been measured for the 0~’ phase The nuclear magnetrc resonance spm lattice relaxation tune, T1, was measured m Ta only. A pulsed field gradient, NMR spur echo technique was utilized to measure D. In both systems, the actrvatron energy mcreases wrth hydrogen concentration while the preexponential factor is not strongly concentratron dependent. The diffusion results are compared with pubhshed values of the macroscopic diffusion coefticrent, D*, obtamed from Gorsky effect measurements Values of the thermodynamic factor [@/k7’)@/+)] are found for selected p and T, where @is the chemrcal potential and p 1s the density of hydrogen atoms These values agree with known determinations of the same factor obtained from the Gorsky effect relaxation strengths, but the agreement wrtb results from solubdrty measurements 1s less satisfactory NMR relaxation is partitioned into conductron electron (T;:) and dipolar (T;:) relaxation rates The observed x dependence of (D/Tld) IS mconsrstent wrth random occupancy of tetrahedral sites, and it 1s suggested that a repulsive mteractron exists between H atoms on nearest nerghbor sites. Recewed 21 October 1980 16.
KINETICS OF CLUSTERING AND PRECIPITATION IN LiF DOPED WITH MgFz J.E Strutt and E. Ldley, Materials Science Group, School of Engmeering and Applied Sciences, University of Sussex, Falmer, Sussex, England
An experimental study of the kmetrcs of clustermg and precipitation m the system LrF -MgF, has been undertaken. The results showed that the pre-plateau region of the ageing curves is due to a homogeneous
ABSTRACTS
OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
with the evident distrrbutions between the prmcipal g values arising from an isotropic randomness at the titamum sites. However, the g parameter drstributrons of the hole resonance, and theu changes during the addition of TiOz indicate the development of Silicate structures in the glasses which are the precursors of the major low temperature crystalline phases The invanance of the hole and electron resonance lmes with pre-crystallrzatron heat treatments indicates that neither the titanium associated structures of the basic silicate structure of the glass are changed by such treatments. Recewed 23 December 1980 Revised 20 March 198 1 9
THE HOPPING MOTION OF THE SELFTRAPPED EXCITON IN NaCl
was investigated wrth X-rays. The sample used in the experrment showed a macroscopic hydrogen density mode, leading to a curvature of the whole crystal plate wrth the o-phase on the concave side and the cy’-phase on the convex side. In addition an o-phase wettmg layer was found on top of the or-phase separated from the bulk cur-phase by a mrxed (Y-Q’ phase regron. In a snnple model therr thickness was determmed to about - 1 0 and - 7.0 m, resp. This thm wetting layer leads to a new interpretation of the phase transitron of H and Nb, mvolvmg the fanuliar long-range elastic mteractron as well as a short-range surface free energy contrrbutron. Recerved 15 December 1980
11.
K. Tammura and N. Itoh, Department of Crystallme Materials Science, Faculty of Engmeermg, Nagoya University, Nagoya 464, Japan. The decay kmetrcs and the yield of the n luminescence from the lowest triplet state of the self-trapped exciton have been studied m NaCl contammg Lr+ ions. It 1s found that the n lummescence band which 1s observed at 6 K 1s replaced by a lummescence band peaked at 3.34 eV above 77 K. The 3.34 eV lummescence band is ascribed to the recombmatron of the relaxed excrton trapped by a Lr+ ion, (V,e),. The decay of the n lummescence induced by an electron pulse and the time change of the lummescence from are explamed in terms of the characterrstrc (vke)Ll equation of the diffusron-limited reaction of the lowest tripled self-trapped excrtons with the Li+ ions. From the analysis of the dependence of the decay rate of the 7r lummescence on temperature and on the Lt+ concentration, we found the drffusron constant D of the lowest tnpled self-trapped exciton in NaCl to be grven by D = D,,e-Ea’kT withD, = 2.13 x 10s3 cm* see-’ and E, = 0.13 eV. The present result can be regarded as the first clear experrmental evidence for the hoppmg drffusion of the self-trapped exciton in alkali halides. The obtamed values of E, and Do are discussed usmg the small polaron theory. The effect of the anharmomcrty on the hoppmg of the self-trapped excrtons 1s suggested to be srgnificant. Received 29 December 1980 10.
CRITICAL POINT WETTING IN NbH,.B, H. Zabel, B. Schonfeld and S.C. Moss, Physics Department, University of Houston, Houston, TX 77004, U.S.A.
The local o--o phase distrtbutron 111a thm Nb smgle crystal loaded with the crrtrcal H-concentratron
ui
THE SOLID STATE REACTION BETWEEN AgI AND Hg12 V Leute and B. Schroder, Institute of Physrcal Chemistry, University of Munster, Schlossplatz 4,440O Munster, Germany.
The kmetrcs of the solid state reaction between AgI and Hg12 1s mvestrgated experimentally by measurmg the thickness of the layer of the oz-Ag2Hg14 product phase as a function of the annealing tune and the reaction temperature. A theoretical expression 1s denved whrch allows the calculatron of the variation of the chemical potentials of the binary components across the product layer consrdermg the vanatron of the product phase composition A value of A0 = 6 KJ mole-’ 1s estimated for the standard affinity for the formation of storchrometrrc Ag, Hg14 from the binary components AgI and Hg12. Recewed 19 December 1980 Revised 20 March 198 1
12.
THE MAGNETIC BEI-IAVIOUR OF DILUTED CrAl ALLOYS I Pop, D. Dadlrlat, T. Petrrsor and A. Gmrgm, Department of Physrcs, Cluj-Napoca University, 3400 CluJ-Napoca, Romania
Magnetic susceptrbrhty as a function of temperature of binary CrAl alloys contammg 0.7, 1.07, 1 35, 1.59, 1.79, 1.98,2.18, 2.84,3.74 and 4.36 at.% Al 1s mvestigated. Alummmm, by alloymg, acts on the Neel temperature of pure chrommm gwmg rrse to a complicated phase diagram The behavrour of the magnetic susceptrbility as a function of temperature, m the ordered phase, for the samples contammg 1 28,2.18 and 2.84 at.% Al 1s found to be temperature independent. In the paramagnetrc region, for the samples contaimng between 1.07
iv
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
and 2.84 at.% Al, it is found a decrease of the magnetic susceptibility as a functron of temperature. Recerved 23 September 1980 Revised 29 March 198 1 13.
ELECTRON TRANSPORT IN SEMICONDUCTORS IN THE PRESENCE OF IMPACT IONIZATION A. Reklaitrs, Semiconductor Physrcs Institute of the Academy of Sciences of the Lithuanian SSR, Vilmus, USSR
The development of impact ionization m semiconductors has been consrdered. A transport equation for the electron drstrrbutron function m the presence of impact ronization has been derived. It has been found that the collisron integral of this equation 1s nonlinear with respect to the distribution function The relatron between the solutions of this equatron and the usual Boltzmann equation have been determmed. A Monte Carlo method for numerical calculations m the presence of impact romzation has been developed. The results of numerical calculations carrred out usmg a srmphfied model of mdmm antimomde are presented Recerved 28 Ju& 1980 Revised 29 March 1981 14.
CORRELATION BETWEEN DEFECT STRUCTURES AND DIELECTRIC CONSTANT IN GALLIA-DOPED RUTILE (TiOZ) E. Iguchr, K, Ogmo and H. Sawatari, Department of Metallurgical Engmeermg, Faculty of Engmeermg, Yokohama Natronal Umversity, Tokiwadai, Hodogaya-Ku, Yokahama, 240 Japan, and R.J .D Tllley , School of Materials Science, Umversrty of Bradford, Bradford, BD7 lDP, West Yorkshire, England
Drelectrrc constants and a.c. resntrvmes of rutrle (TrO,) doped with galha (Ga, 0,) have been measured as a function of frequency m the range 30-60 kHz at 20” C. The specrmens were prepared by heating rutile smgle crystals on Gaz 0s pellets, at 1300’ C, in air for various times. The dielectric constants depend on the frequency of measurement. In the c axis, the drelectric constant at low frequencies (30-100 Hz) mcreases as the sample heating tune is extended to 1 week, but rt decreases raptdly when the heating time 1s prolonged over 1 week. However, m the a axis, the dielectric constant does not change from the value of the starting materral, being independent of the heatmg trme. Besides drelectnc measurements, the defect structures were determmed using transmissron electron mrcroscopy, which showed that low concentrations of planar faults
Vol. 40, No. 5
on (120) planes occur. The changes m dielectric constant are mterpreted as bemg due to space charge effects associated with Ga3+ ions located in the tunnels which he parallel to the rutrle c axis. Calculatrons are also mcluded which show why other defects m the crystals have no effect on the value of the dielectric constant compared to pure r-utile. Received 17 December 1980 Revised 3 1 March 198 1 15.
DIFFUSION AND NMR SPIN LATTICE RELAXATION OF ‘H IN 0~’TaH, AND NbHZ F.E. Mauger, W.D. Wrlhams and R.M. Cotts, Laboratory of Atomic and Sohd State Physrcs, Cornell University, Ithaca, NY 14853, U.S A
The concentratron and temperature dependence of the self diffusion coefficient, D, of H m Group V transrtron metals Nb and Ta has been measured for the 0~’ phase The nuclear magnetrc resonance spm lattice relaxation tune, T1, was measured m Ta only. A pulsed field gradient, NMR spur echo technique was utilized to measure D. In both systems, the actrvatron energy mcreases wrth hydrogen concentration while the preexponential factor is not strongly concentratron dependent. The diffusion results are compared with pubhshed values of the macroscopic diffusion coefticrent, D*, obtamed from Gorsky effect measurements Values of the thermodynamic factor [@/k7’)@/+)] are found for selected p and T, where @is the chemrcal potential and p 1s the density of hydrogen atoms These values agree with known determinations of the same factor obtained from the Gorsky effect relaxation strengths, but the agreement wrtb results from solubdrty measurements 1s less satisfactory NMR relaxation is partitioned into conductron electron (T;:) and dipolar (T;:) relaxation rates The observed x dependence of (D/Tld) IS mconsrstent wrth random occupancy of tetrahedral sites, and it 1s suggested that a repulsive mteractron exists between H atoms on nearest nerghbor sites. Recewed 21 October 1980 16.
KINETICS OF CLUSTERING AND PRECIPITATION IN LiF DOPED WITH MgFz J.E Strutt and E. Ldley, Materials Science Group, School of Engmeering and Applied Sciences, University of Sussex, Falmer, Sussex, England
An experimental study of the kmetrcs of clustermg and precipitation m the system LrF -MgF, has been undertaken. The results showed that the pre-plateau region of the ageing curves is due to a homogeneous