Enhancement of the electron mobility with infrared photoexcitation in Si: Te at low temperatures

Hall measurements on Te-doped silicon (N _Te 10¹⁶ cm^–3) have been performed in the temperature range between 10 K and 300 K with infrared photoexcitation of electrons into the conduction band. The samples exhibit electron Hall mobilities which are increased by approximately 50% compared to measurements in the dark. The increased electron mobility can be correlated with an increased electron population of shallow donor levels by photoexcitation. Coulomb scattering due to charged shallow donor centers is converted into less efficient dipole scattering (Te-acceptor pairs) by the light-induced redistribution of electrons.     

Intrinsic carrier concentration in Hg1−xCdxTe

The effective mass of heavy holes has been determined on the basis of simultaneous analysis of the Hall coefficient and conductivity data obtained in the temperature region 100–300 K on well characterized p-type Hg_1–x Cd_xTe (x0·2) samples. Its value is 0·7m₀. The calculation of intrinsic carrier concentration for 0·19 x0·3 and 50 Kg T 300 K has been carried out using the above value of the effective mass of holes, Hansen's expression for the band gap and momentum matrix element from magneto-optical measurements.     

Electrical properties of n-type Si layers doped with proton bombardment induced shallow donors

Sheet Hall coefficients and resistivities of n-type Si layers doped with shallow donors produced by proton bombardment have been measured between 35 and 300°K. The donor ionization energy is (26 ± 1) meV. The donor concentration profile has been determined.     

Charge carrier governed temperature dependence of the electric field gradient for111Cd in tellurium

Using the TDPAC-method with the proble nucleus¹¹¹Cd the electric quadrupole interaction (QI) in the trigonal semiconductor Te has been investigated in the temperature range 77 KT655 K. In contrast to most metals the quadrupole frequencyv _Q increases with increasing temperature. This is a consequence of the fact that in metals the charge carrier density is temperature independent, whereas in semiconductors it strongly increases with temperature. A comparison between the temperature variation of the quadrupole coupling constantv _Q and that of the charge carrier density leads to the conclusion that the QI in Te is governed by changes in the free electron density.     

Heterodiffusion of Cr in molten Fe in the temperature range 1800 to 1970 K

Heterodiffusion of Cr has been studied using the method of thin layer and the radionuclide⁵¹Cr. The diffusion characteristics determined from the experimental results in the temperature range 1800 KT1970 K areD _o=1·59×10^–2 cm²/s andE=22·3±1·6 kcal/mol. The experimental method is discussed in detail and the results are compared with those of other authors.     

Specific heat of neutron-compensated heavily doped Si:P near the metal-insulator transition

The specific heat of neutron-irradiated heavily doped Si:P (3.3·10¹⁸ cm^–3Nd7.3·10¹⁸ cm^–3) was measured between 0.07 and 3K and in magnetic fields between 0 and 6T. The compensation ratio was varied systematically by isochronal annealing. Characterization was done by temperature dependent measurements of Hall coefficient and electrical resistivity. The specific heat displays a minimum of the linear coefficient at the carrier concentration where the P impurity band is starting to be occupied. The concentration dependence of localized moments inferred from Schottky anomalies can be interpreted in terms of localized magnetic moments arising from the defect structure introduced by the irradiation and from P-derived electrons. As in uncompensated Si:P, local moments survive on the metallic side of the transition.     

Magnetic properties of Nd3+ in Nd−Ba−Cu−O-compounds

Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd_1+y Ca _v Ba_2–y–v Cu₃O _x (0y0.5; 0v0.25; 6x7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofT _c. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd³⁺-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd³⁺ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data.     

Valence change of europium in the Eu(Ir1−x Pd x )2Si2 silicides

Eu(Ir_1–x Pd _x )₂Si₂ solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr₂Si₂-type structure. X-ray diffraction data, magnetic susceptibility and¹⁵¹Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu²⁺ to Eu³⁺ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance.     

β-Relaxation and low-temperature specific heat in (KBr)1−x(KCN)x

The specific heat in (KBr)_1–x(KCN)_x has been measured for concentrations 0.00x0.93 and for temperatures 2 KT50 K. In addition, the dipolar relaxation phenomena were studied using dielectric spectroscopy. The relaxation behaviour was parametrized assuming a Gaussian distribution of energy barriers and the mean activation energies, the distribution widths, and the attempt frequencies have been determined as a function of the CN^– concentration. With these parameters the linear and the excess specific heat contributions were calculated and compared to the calorimetric results.     

LaAg x In1−x

The structures of LaAg _x In_1–x alloys withx=0.75, 0.89 are determined by neutron diffraction on powder samples. The space group isI4/mmm (D _4h ^/17 ). The lattice constants splitting, the order parameter and the mean square vibrational amplitudes of the atoms are given in the temperature range from 20 KT300 K.     

Anisotropic low-temperature heat transport in YBa2Cu3O6.9 single crystal

We report measurements of the low-temperature thermal conductivity of YBa₂Cu₃O_7– (0.1) single crystals (T _c =84 K) both parallel ( ^{a, b} ) and perpendicular ( ^c ) to the CuO₂ planes. Whereas ^c (T) is found to be identical, within experimental resolution, with the phonon contribution _ph (T), ^{a, b} (T) contains an additional term linear in temperature,AT. We ascribeAT to the contribution of unpaired electronic carriers residing in the chain layers. Measurements performed in external magnetic fieldsB8 T support this interpretation. Our observations can be explained by an internal multilayer (IML) model in which it is assumed that strong superconductivity is generated within the CuO₂ layers and weak superconductivity is induced in the chain layers by the proximity effect. The fit of the experimental results to the IML model reveals that approximately 15% of the electronic carriers remain unpaired in YBa₂Cu₃O₇ belowT=1 K.     

High-temperature conductivity study on single-crystal C60

We report about dc, ac (100Hzv100kHz) and contactless microwave (10 GHz) conductivity studies on C₆₀ crystalline bulk material from room temperature to 850 K. The high temperature regime is governed by an activated behavior with a frequency and sample independent activation energy of about 0.9 eV. The low temperature regime exhibits a frequency dependent and weakly temperature dependent conductivity due to extrinsic properties.Anomalies in the heating curves of virgin samples (dynamical vacuum conditions) in the temperature ranges 560 K and 740 K are ascribed to the desorption of oxygen.     

Anomalies of the static dielectric constant of Pb1−x Ge x Te

The static dielectric constant of Pb_1–x Ge _x Te (0x0.05) has been determined from differential capacitance measurements on Schottky-barriers in the temperature range of 4.2–300 K. A comparison with data deduced from the phonon frequencies via the Lyddane-Sachs-Teller relation shows substantial discrepancies which are attributed to lattice defects.Work supported by Jubiläumsfonds der Österreichischen Nationalbank     

Properties of yttrium-iron-metalloid glasses

We report the results of measurements on metallic glasses of the form Y₆₆(Fe_1–x M _x )₃₄. For M = B we find that there is an extended range of glass formation (0x0.40) and that properties such as atomic density, electrical resistivity, microhardness, and thermal stability are functions ofx. For M = C, Si, or Ge we find a restricted range of glass formation (0 x0.10) and no significant changes in the properties of the glasses. Using Fe⁵⁷ Mössbauer effect spectroscopy we find that the M = B case is again unique in that the structure of the glass is sensitive to B content. We relate the differences in glass formation for the M = B and M = C, Si, Ge glasses to the existence of Y rich compounds in the C, Si, and Ge cases and the lack of such compounds in the M = B case.     

Carrier scattering mechanisms in P-type indium selenide

Carrier scattering mechanisms in p-indium selenide are investigated by means of the temperature dependence of the Hall mobility (160–500 K) and thermopower (200–300 K). An anomalous behaviour of the Hall voltage, which changes sign below 215 K, is interpreted through the existence of planar aggregates of ionized shallow donor impurities that create potential wells behaving as deep donors and in which a low concentration of two-dimensional free electrons can exist. This fact is taken into account through equations for two-carrier Hall effect. Holes are found to be predominantly scattered by anA ₁ homopolar phonon with an energy of 27.8 meV. From thermopower results, the density of states effective mass in the valence band is determined,m _dv ^* =(1.5±0.2)m ₀.     

Measurement of the refractive index and optical absorption spectra of epitaxial bismuth substituted yttrium iron garnet films at uv to near-ir wavelengths

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y_3–x–y Bi _x Pb _y Fe_5–z Pt _z O₁₂ films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

M?ssbauer effect in superconducting tin-europium-molybdenum-sulfides

Mössbauer spectra of¹¹⁹Sn in Sn_1–z Eu _z Mo₆S₈ (z=0, 1/3, 2/3) have been measured in the temperature range 4.9 KT293 K. The spectra consist of a quadrupole doublett with unequal intensities at all temperatures. The Debye-Waller factor, the isomeric shift and the asymmetry of the intensity of the quadrupole components show irregularities between 50 K and 110 K which are interpreted as arising from a structural phase transition. The temperature dependence of the Debye-Waller factor can be approximated by a simple phonon spectrum. No quantitative explanation can be given for the large values of the asymmetry. Evidence is presented that this behavior is connected with the properties of the librational modes of the Mo₆S₈-units in the crystal.     

Measurements of π+p,K+p and pp elastic scattering)

The paper presents the results on differential cross sections for elastic scattering of 7⁺-, K⁺-mesons and protons on protons in the 4-momentum transfer squared range 0·08 ¦t¦ 1·0 (GeV/c)² and incident particle momentum of 29 and 43 GeV/c for pions and kaons and 29, 43, 50 and 65 GeV/c for protons. The measurements were taken with the spectrometer Sigma, installed in the positive beam of the IHEP accelerator.Presented by F. A. Yotch at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.The authors would like to express their gratitude to A. A.Logunov, Yu. D.Prokoshkin, L. D.Soloviev and V. A.Yarba for their support of this experiment. We are indebted to CERN Administration for giving us a permission to use a part of equipment of the CIBS spectrometer and to W.Kienzle for useful discussions.     

Phases and phase transitions in the mixed molecular system (NaCN)1−x(KCN)x

The phase diagram of (NaCN)_1–x(KCN)_x was examined by neutron powder diffraction in the temperature range 5K T300 K. Several non-cubic low-temperature phases were identified for concentrationsx<x _c1=0.15 andxx _c2=0.89. Lattice parameters and ferroelastic deformations were determined from the observed powder patterns. The phase transformations were characterized following the temperature dependence of the appropriate order parameters.