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We measured the peak effect in the magnetic hysteresis loop of an untwinned ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ crystal in the vicinity of the critical temperature and studied its temperature, time, and angular dependence. The location of the peak is determined by the component of the field along the c direction. The pinning force density ${\mathit{F}}_{\mathit{p}}$(B) is scaled into a single curve for all measured isotherms (75--87 K) and time scales (4--1500 sec), and its functional form reflects the observed peak effect. The scaling field is related to the irreversibility field of oxygen-deficient regimes. The results indicate that pinning in this system is due to inhomogeneity of the oxygen deficiency and that the peak is related to the formation of a percolationlike network of reversible regimes.

Optically detected and conventional spin resonance investigations have been successful in determining the structure of cation vacancy-donor pairs (A-centers) and anion vacancies ( V Te ) in CdTe. Investigations in the ternary alloy systems Cd1−xZnxTe for the complete range of x show that the A-center binding energy is almost independent of the composition. In CdTe the VTe+/0 level position is 0.2 eV above the valence band and correlation to a deep luminescence band at 1.15 eV can be drawn. In the alloys this photoluminescence band closely follows the conduction band from CdTe to ZnTe. Studies of the spectroscopic g- values of the shallow donors in Cd 1−x Zn x Te show that they shift linearly from -1.69 in CdTe to -0.4 in ZnTe.

CdTe single crystals have been grown using either the Bridgman or the travelling-heater technique. Crystals doped with indium or chlorine were compared with those without any intentional dopant. With high resolution atomic absorption spectroscopy analysis it was possible to measure the effective segregation coefficient of indium down to concentrations of 3 × 10 15 In atoms cm−3. Higher amounts of indium resulted in n-type conductivity but, with less indium than 1 × 10 15 cm −3 , crystals were p type, as is always the case for undoped crystals. Photoluminescence spectra taken from as-grown samples and from samples annealed at 380°C or 780°C with subsequent quenching revealed the A centre but require reconsideration of the role of this complex in the compensation models.

We report on the identification by electron paramagnetic resonance (EPR) of the atomistic and electronic structure of the Te vacancy (${\mathit{V}}_{\mathrm{Te}}$) in CdTe. The resolved, isotropic hyperfine interaction with the four nearest Cd neighbors, the isotropic g value of g=2.000\ifmmode\pm\else\textpm\fi{}0.001, and the long spin-lattice relaxation time serve as a conclusive identification of the F center. From photo-EPR investigations we obtain two threshold energies for the recharging of ${\mathit{V}}_{\mathrm{Te}}$. Its electron ionization transition from the neutral to the positive charge state at 1.4 eV determines the energetic level at ${\mathit{E}}_{\mathit{V}}$+0.2 eV. It acts as a single donor in CdTe.

The symmetry and density of unoccupied states of twin-free YBa{sub 2}Cu{sub 3}O{sub 7} and YBa{sub 2}Cu{sub 4}O{sub 8} single crystals have been investigated by orientation-dependent x-ray absorption spectroscopy at the O 1{ital s} edge, using a bulk-sensitive fluoresence-yield-detection method. In conjunction with earlier results obtained by electron-energy-loss spectroscopy, the relative density of unoccupied states for different oxygen sites has been derived. Comparison with local-density energy-band-structure calculations shows reasonable agreement with the experimental results.

We investigated various areas of impurity-free YBa2Cu3O7−δ single crystals with Raman spectroscopy. A definite correlation between the appearance of the group- theoretically forbidden chain-related Raman lines at 232 and 598 cm−1 and the superconductivity-induced self-energy effects observed for the 340 cm−1B1g-like mode was established: Disorder in the chains in pure crystals has a similar effect as the introduction of impurity atoms, both leading to an increased gap value for 2Δ/kTc as deduced from the phonon self-energy effects. The absence of the forbidden chain modes in the Raman spectra may be used as an extremely sensitive quality criterion of impurity-free crystals.

We report investigations of optical nonlinearities in the cubic II–VI compounds ZnSe and ZnTe. Studies of luminescence and reflectivity at low excitation and at low temperatures were used to characterize the quality of the samples. Carefully thinned and etched samples show spectra comparable to the ones observed on cleaved surfaces. Measurements of luminescence at high excitation and at low temperatures show spectra which leads to the assumption that an electron-hole plasma is created. With pump and probe beam spectroscopy we obtained further informations about the formation of an electron-hole plasma. The results concerning optical gain are compared with previous measurements on CdS and CdSe and with results for ZnSe and ZnTe which are obtained with the strip length method by other authors.

Summary form only given. The electronic structure of CuO/sub 2/ planes and CuO chains in single domain crystals of YBa/sub 2/Cu/sub 3/O/sub x/ has been investigated as function of oxygen concentration ( 6 /spl les/ x /spl les/ 7 ) using polarization dependent x-ray absorption spectroscopy on Ols and Cu2p levels. The polarization dependent observation of unoccupied states with O and with Cu orbital character parallel to the a, b, and c axes of the crystals allows the determination of hole states in Cu 3d/sub y/sup 2//-/sub z/sup 2// and O 2p/sub y,z/ orbitals in the CuO/sub 3/ chains. The number of holes is found to be correlated with the superconducting transition temperature and is no linear function of x.

Both the cadmium vacancy (Vcd) and the tellurium vacancy (VTe) in CdTe are identified by means of electron paramagnetic resonance (EPR). The VCd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of VTe+ reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours.Photo-EPR measurements locate the 0/+ state of VTe at Ev + 0.2 eV and the 2−/− acceptor level of VCd to be situated less than 0.47 eV above the valence band.

The symmetry and density of unoccupied states of YBa{sub 2}Cu{sub 3}O{sub 7} YBa{sub 2}Cu{sub 4}O{sub 8} have been investigated by orientation dependent x-ray absorption spectroscopy on the O 1s edge using a bulk-sensitive fluorescence-yield-detection method. It has been found that the O 2p holes are distributed equally between the CuO{sub 2} planes and CuO chains and that the partial density of unoccupied O 2p states in the CuO{sub 2} planes are identical in both systems investigated. The upper Hubbard band has been observed in the planes but not in the chains in both systems. 18 refs.

Certain transition metal silicides display interesting thermoelectric properties at high temperatures. β-FeSi 2 is one of those and has been investigated in depth. Similar properties at high temperatures can be expected in the case of OsSi 2 and this was confirmed by X-ray investigation, measurement of conductivity, thermopower, reflectivity and the mechanical properties of sintered specimens. This paper records the results of investigations of the Os-Si phase diagram and crystal growth from this system. Better results were achieved at significantly lower growth temperatures when PdSi was used as the solvent.

The effective distribution coefficients of Fe and Si in LiNbO3 single crystals were determined using atomic absorption spectroscopy. For the determination of Si-concentration, the graphite furnace technique was used. In undoped crystals, the impurity levels of Si, Fe, Cu and Zn were measured. The influence of Si ions on the fixation process of phase holograms in LiNbO3-crystals is briefly discussed.

With thermoanalytical methods the solubility of rare earth salts in fluxes used for the growing of single crystals are investigated and the systems YVO4NaVO3 and REPO4Pb2P2O7 (RE = Tb to Lu, Y) are measured. The various REPO4 show different solubilities. Borax and lead oxide as additions to the fluxes increase the solubilities of the vanadates and phosphates respectively. The results allow the exact determination of starting temperatures and compositions for the flux growth of better crystals of these compounds. Mit Hilfe thermoanalytischer Methoden werden die Loslichkeiten von RE-Salzen in Flusmitteln untersucht, die zur Kristallzuchtung dieser Verbindungen dienen. Gemessen werden die Systeme YVO4NaVO3 und REPO4Pb2P2O7 (RE = Tb bis Lu, Y). Die verschiedenen REPO4 zeigen unterschiedliche Loslichkeiten. Borax und PbO-Zusatze zu den Flusmitteln fur Vanadate und Phosphate erhohen deren Loslichkeiten in den betreffenden Flusmitteln. Aus den Mesergebnissen lassen sich die Versuchsparameter, wie Anfangstemperaturen und Zusammensetzung, zur Zuchtung besserer Kristalle dieser Verbindungen entnehmen.

Fixation of phase holograms in LiNbO3 is observable above 100 °C and is caused by transport of ions. From an analysis of the fixation kinetics a concentration of these ions of 2 × 1017 cm−3 and a diffusion constant at 180 °C of 5 × 10−13 cm2/s are determined. Si and OH ions suggested previously to be associated with fixation do not seem to be responsible for fixation. The development of fixed holograms by uniform illumination is based on a modulation of the optical absorption produced during fixation. Das Fixieren von Phasenhologrammen in LiNbO3 wird oberhalb 100 °C beobachtet und wird durch den Transport von Ionen verursacht. Aus der Analyse der Kinetik des Fixierens wird die Konzentration dieser Ionen zu 2 × 1017 cm−3 bestimmt und ihre Diffusionskonstante bei 180 °C zu 5 × 10−13 cm2/s. Si- und OH-Ionen, die bereits mit der Fixierung in Zusammenhang gebracht wurden, scheinen nicht fur die Fixierung verantwortlich zu sein. Die Entwicklung fixierter Hologramme durch gleichmasige Belichtung beruht auf einer Modulation der optischen Absorption, die beim Fixieren entsteht.

A study has been made of the chemical reactions occurring during the determination of molybdenum by electrothermal atomic absorption spectroscopy. X-ray diffraction and electron microscopy investigations were applied. It is shown, that at temperatures of ca. 1300 K, Mo2C is formed by reduction of MoO3. At 1950 K, Mo2C is transformed into MoC. The rate of the phase transformation is rather slow. Therefore, at fast heating rates, both compounds MoC and Mo2C reach the atomization step.

Crystals of CdS doped with Zn, Pb, Ag and crystals of CdTe doped with Pb have been grown from the vapour phase in perforated ampoules. The doping profiles measured by atomic absorption spectroscopy correspond with the transport model developed in part I. A drastic purification effect is found in the case of Pb and Ag, whereas a slight accumulation of Zn in CdS is observed. The quantitative evaluation of the Pb and Ag profiles yields the coefficients of vapour diffusion (D0) and interfacial segregation (k). The k values are determined without any knowledge of impurity vapour pressures. The total leakage loss is found to be the essential controlling parameter of the refining which is most efficient near the leak hole. In addition, the model of impurity transfer is modified to describe the effect of the leak hole on the stoichiometry of the growing crystal, if the composition of the source is non-stoichiometric.

The physical vapour transport of impurities in semi-closed (perforated) ampoules is treated in terms of a one-dimensional model. The theory considers the growth of II–VI compounds under steady state conditions. In addition to the diffusive-advective mass transfer to the crystal, the leakage loss is taken into account. The concentration of an impurity in the growing crystal is given as a function of the interfacial segregation coefficient and of adjustable parameters. The model leads to conditions of controlled, steady purification and doping during the growth process. Also it offers a method to determine the interfacial segregation coefficient without any knowledge of the impurity vapour pressure.

The growth and dissolution rates of YPO 4 and DyPO 4 crystals in high temperature solutions of Pb 2 P 2 O 7 are determined for various saturation temperatures. The R (α) curves are linear, indicating the volume transport of the solute to be the rate limiting step. The dissolution rate is nearly 30% greater than the growth rate which is evidence for an additional resistivity in the growth process.

Raman scattering and superconductivity of titanium nitride with various N deficiencies have been investigated. While in stoichiometric superconducting TiN second-order Raman scattering is predominant, first-order Raman scattering increases with increasing N deficiency. The first-order Raman spectrum which agrees well with the phonon density of states shifts to higher frequencies when the N deficiency grows. This frequency shift is particularly strong at small N deficiencies (\ensuremath{\sim}5%) and is coupled with a drastic drop of ${T}_{c}$. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 ${\mathrm{cm}}^{\ensuremath{-}1}$ in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies $〈{\ensuremath{\omega}}^{2}〉$ from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric Ti${\mathrm{N}}_{0.55}$ and TiC are discussed.

The series of the title compounds were prepared by solid-state reactions. The phase transitions between room temperature and 1450 °C were investigated by DTA and X-ray diffraction. All compounds undergo at least one reversible phase transition in the solid state. The Rb containing compounds, with the exception of those with Cd and Zn, show no liquid phase up to 1450 °C. The phases formed crystallize with various structures which can be described partly as distorted olivine, LiKSO4, CsZnPO4 or glaserite. RbCdPO4 shows an incommensurate structure with a one-dimensional modulation.

Using an EFP absorption spectrometer the pair interaction of Yb3+ ions was stukdied in YAsO4 crystals. Also an investigation of the relaxation behaviour was performed concerning with the temperature and angular dependence of hte relaxation times of the isolated ions. The relaxation is partially affected by cross relaxation between the single ions and the Yb3+ ion pairs. The direct process at the lowest temperatures is bottlenecked. Mit Hilfe eines EPR-Absorptions-Spektrometers wurden die APaarwechsolwirkung von Yb3+ Ionen in YAsO4-Kristallen und das Relaxationsverhalten (Temperatur - und Winkelabhangigkeit der Relaxationszeiten) der Einzelionen untersucht. Teilweise sind CrossRelaxationen zwischen Einzelionen und lonenpaaren zu beobachten. Der direckte Prozes ist phonogehemmt.

Single crystals of rare-earth orthophosphates (RPO4), arsenates (RAsO4), and vanadates (RVO4) have been grown by a flux method with use of an oscillating-temperature procedure. Crystals having the dimensions 1.5 × 1 × 15 mm, 1 × 1 × 6.5 mm, and 3 × 0.5 × 7 mm, respectively, have been produced in five-day runs. Lattive parameters of (Sc,Er)VO4 single crystals and of (Sc,Er)PO4 powders with various doping ratios have been precisely determined.

The magnetic properties of DyAsO4 were investigated by specific heat and magnetic moment measurements. The specific heat shows two λ-type anomalies, one at TN = 2.44 K caused by a magnetic phase transition, and the other at Tc = 11.2 K. Magnetic measurements show an antiferromagnetic ordering perpendicular to the optical axis with magnetically nonequivalent a- and a′-axes. Exchange integral and critical parameters were determined in different ways and compared with theory. The splitting of the two lowest components (Kramers' doublets) which is constant above Tc becomes temperature dependent below Tc; it increases with decreasing temperature and originates from a cooperative phenomenon. Die magnetischen Eigenschaften von DyAsO4 wurden durch Messung der spezifischen Warme und der Magnetisierung untersucht. Der Verlauf der spezifischen Warme zeigt zwei λ-Anomalien, eine bei TN = 2,44 K, verursacht durch einen magnetischen Phasenubergang, und eine weitere bei Tc = 11,2 K. Die magnetischen Messungen ergaben eine antiferromagnetische Ordnung senkrecht zur optischen Achse mit magnetisch nicht mehr aquivalenten a- und a′-Achsen. Austauschintegral und kritische Parameter wurden auf verschiedene Weise bestimmt und mit der Theorie verglichen. Die Aufspaltung der untersten zwei Komponenten (Kramers-Dubletts), die oberhalb Tc konstant ist, wird unterhalb Tc temperaturabhangig; sie wird groser mit abnehmender Temperatur und hat ihren Ursprung in einem kooperativen Phanomen.

The influence of a magnetic field on the magnetic structure of DyVO4 has been studied on a single crystal at 1.8 K in fields up to 15 kG. At 3.0 kG we observed a domain reorientation along the applied magnetic field. A spin-flip transition to a ferromagnetic state could not be observed within our experimental range.

Density and surface tension of solutions of DyPO4 and YPO4 in molten Pb2P2O7 have been measured in the temperature range from 1170 to 1470 K.

Optical bistability (OB) has potential applications in optoelectronics [1]. Beside electronic OB, which is usually fast, also photo-thermal OB often has been investigated [1]. Its main disadvantage are switching times in the μs-ms regime. In particular thin (a few μm) CdS single crystal platelets show photothermal OB due to induced absorption at room temperature at 514nm.

X-ray powder diffraction measurements at low temperatures have been carried out on TbAsO4. A distortion of the originally tetragonal unit cell along the 〈110〉 directions could be observed at temperatures below 26 K. The transition was found to be most probably of second order.