Piezoelektrische und elastische Eigenschaften von Triglycinselenatkristallen im Bereich des Phasenüberganges

The piezoelectric constants d₂₁, d₂₃, d₂₅ and the elastic constants S₁₁, S₁₅, S₃₃ and S₃₅ of triglycine selenate are measured by the resonance method in the region of phase transformation. The elastic and piezoelectric constants are shown to have sharp maxima in the Curie point. The influence of a constant electric field on the temperature dependence of the piezoelectric constant d₂₃ and of the elastic constant S₃₃ is studied as well as the dependence of the mentioned constants on the intensity of a constant electric field at temperatures below and above the Curie temperature. A considerable increase of the elastic constant S₃₃ is found in weak electric fields of the ferroelectric phase. The electrostrictional coefficients Q₂₁, Q₂₃ and Q₂₅ are determined by means of the piezoelectric constants, spontane polarisation and dielectric receptivity. The found experimental dependences are explained on the base of the character of the domain structure of this crystal.     

Wachstumsformen von tetragonalen Erdalkaliwolframaten in Schmelzlösungen und deren Deutung

Investigations on solubility of CaWO₄ in NaCl melts (ANIKIN ) were extended to BaWO₄ and SrWO₄. – Crystals of tungstates of Ca, Ba, and Sr from NaCl and KCl fluxes respectively were grown at temperatures from 950 to 650°C at cooling rates from 2 to 50 grd. h⁻¹. Marked differences in the forms of these tungstates did not occur. Among many whiskers bipyramidal crystals grew with dendritic, sceletal and hollow transitions forms. The theoretically calculated morphological succession (PBC model) is realised by the faces of the whiskers and platelets ([110] and [100] zones). The remaining crystals – due to face specific adsorption – show other forms similar to those in nature. – Verneuil grown crystals, however, developed – free, from adsorption phenomena – {110} and {001} forms respectively.     

Modelle und Eigenschaften von Korn- und Phasengrenzen

Models about the structure of grain boundaries in pure metals, alloys and of phase boundaries between two crystals of different elements are known. Geometrical and energetical interpretations of these models are discussed. It is tried to establish the structure of grain boundaries by an energetical method. With the results of these theoretical works you can better interpret the experimental results from oriented bicrystals. But the direct investigation of the influence of grain boundaries in polycrystals will be also necessary in future.     

Bandstruktur und thermoelektrische Eigenschaften von Wismut-Antimon-Legierungen

The authors investigate the influence of the electronic band structure on the thermoelectrical properties of Bi_xSb_1–x-alloys (0 ≦ (1–x) ≦ 1). For alloys with a high figure of merit the differential thermoelectric power and the ratio σ/k (σ: electrical conductivity, k: thermal conductivity) give an equal share to the increase of the figure of merit (in relation to pure bismuth). It become evident that the descrease of ratios of mobility for free carriers with different sign is overcompensated by means of modifications of the partial Seebeck coefficients. This is a result of changes in the electronic band structure and in the position of the Fermi level in an m-band-model with m > 2, impairing the electrical conductivity and the thermal conductivity in different wise.     

Die Herstellung und einige Eigenschaften von reinen und dotierten BaTiO3-Einkristallen

Colourless BaTiO₃-monocrystals were prepared by slowly cooling down from 1300°C a mixture of BaTiO₃, Ba₂TiO₄ and BaCl₂ in a Pt-crucible under Ar-atmosphere. The crystals have a Curietemperature of 132°C. Partial substitution of Ti by Nb or V decreases the Curietemperature of BaTiO₃. The dependence of Curie-temperature from the concentration of the foreign ions was investigated.     

Untersuchungen an Systemen aus Salzen und gemischten Lösungsmitteln (XII) Kristallographische Eigenschaften und Zersetzung der Methanolsolvate des MgSO4

This paper informs on microscopic and IR-spectroscopic properties of MgSO₄ · 2 CH₃OH and MgSO₄ · 2 H₂O · 2 CH₃OH, structural composition, microscopic observation of thermal decomposition and some kinetic values of desolvating process.     

Herstellung und elektrische Eigenschaften von dotiertem ZnSiP2

The properties of ZnSiP₂ crystals prepared by adding of Ga and In to the melt differ essentially from that of undoped samples. Especially the activation energies determined from the temperature dependence of the Hall coefficient prove that in both cases a real doping with shallow impurities has taken place. Ga and In act as donors suggesting the conclusion that Ga and In atoms substitute Zn atoms. The existence of strong electrical inhomogenities in a part of the samples is discussed.     

Dielektrische und akustische Eigenschaften von Ag5SbS4

Measurements of the temperature dependences of the real and imaginary part of the complex dielectric permittivity at microwave frequencies together with the damping constant and the velocity of ultrasonic waves in Ag₅SbS₄ crystals have been made. The Peculiarities of the crystals grown and the nature of the phase transition in Ag₅SbS₄ are discussed.     

Zur dynamischen Untersuchung elastischer und elektromechanischer Eigenschaften von Kristallen

For the determination of elastic and piezoelectric coefficients as well as of the mechanical quality factor the piezoelectric resonator has proved a most simple and exact method. In this paper some possibilities for increasing the accuracy of this method and its application on weak piezoelectric crystals as well as for the determination of higher order elastic coefficients are shown. These procedures can also be used for dynamic measurements on electrostrictive materials (electrostrictive resonator).     

Züchtung und Eigenschaften von Mangan-, Kobalt-und Zinkmanganatkristallen

Crystals of the manganates of manganese, cobalt, zinc have been grown from a flux solution of PbO-PbF₂ by slow cooling. Their lattice constants are compared with dates of sintered products (from literature). It resulted by comparison of the densities obtained by X-ray and by pycnometer that the deficit of oxygen is caused by anionic vacancies in the lattice.     

Die Eigenschaften des leitfähigen Durchschlagkanals und sein Einfluß auf den bistabilen Schalteffekt in Cu2O

The current-voltage-characteristics and the temperature dependence of the thermopower and of the resistivity are measured on Cu₂O bistable switching elements in the lowresistance state. The behaviour of the low-resistance state is essentially determined by narrowings of a quasi-metallic copper filament. The narrowings result from the contact of copper particles inside the Cu₂O matrix. The behaviour of return switching into the highresistance state may be deduced from the structure of the filaments. The statistical fluctuations of the switching parameters are explained by the properties of the on-switching and off-switching process.     

Darstellung,Struktur und Eigenschaften von Nb-, Mo-, W- und Ru-dotiertem VO2

Monocrystals of doped VO₂ having the general composition V_1–xMe_xO₂ were prepared by chemical transport with TeCl₄. A summary of the morphological, structural, electric and magnetic properties is given. The habit of the doped crystals depends on the doping factor x. The boundary surfaces are {110}-prismatic and {111} pyramidal ones. At x = 0.04 the lattice constants change rapidly between the monoclinic M1-and the tetragonal R-phase. The typical change of resistance, which amounts four orders of magnitude for pure VO₂, and the transition temperature T_c decrease with increasing x.     

Herstellung und ausgewählte physikalische Eigenschaften von ZnSiP2

Undoped ZnSiP₂ crystals grown by different methods (vapour phase transport, solution growth) show in part considerable differences in their physical properties. The connections between growth, quality of the basic materials and the physical properties of ZnSiP₂ will be shown. Measurements of Hall effect, resistivity, luminescence and backscattering of protons yielded informations about the perfection and homogenity of the crystals and about the impurities and recombination centres characteristically for the various growth methods. The influence of doping by different elements on the properties of solution grown ZnSiP₂ crystals was investigated.     

Physikalische Eigenschaften von nach einer modifizierten Kyropoulos-Methode gezüchteten NaCl- und KCl-Kristallen

The physical properties of NaCl and KCl crystals prepared from melts by the Kyropoulos method are described. The material was firstly refined by phosgen (COCl₂) by which the anion impurities were removed from the melt. The measurements of the absorption in UV and IR region, the microhardness and CRSS, the dislocation densities, the ionic conductivity and the study of the kinetics of colour centres show that crystals prepared by the described modified Kyropoulos method are not only free from OH⁻ ions but also from all other foreign anions with oxygen.     

Eigenschaften und Kristallzüchtung von Oxiden mit Halbleiter-Metall-Übergängen

This review reports the possibilities of crystal growth for oxides of vanadium and titanium having semoconductor-to-metal transitions. The favoured methods of crystal growth, chemical transport reactions, and the flux melts are discussed in detail.     

Die Molekül- und Kristallstruktur des N-Methyl-piperidinium-acet-para-brom-anilid-jodid

N-Methyl-piperidinium-acet-para-bromo-anilide-iodide crystallizes in the triclinic space group P 1 with two formula units C₁₄H₂₀N₂OBrJ and two H₂O molecules in the unit cell. The lattice constants are a = 8.950 Å, b = 14.721 Å, c = 7.440 Å, α = 80.19°, β = 112.57° and γ = 106.82°. The molecular structure of the compound was determined by the X-ray structure analysis and the interaction between the molecules in the crystal was investigated. Especially the influence of the water in the crystal on the form of the molecule was analysed.