Single crystals of congruently and incongruently melting oxides have been grown by the optical floating zone (OFZ) and traveling solvent floating zone techniques. Both relatively low-cost methods work especially well for oxides melting above the maximum operating temperature of conventional crucibles or that were previously impossible to grow due to crucible oxidation or reaction of the melt with the crucible material. For incongruently melting oxides, solvents with experimentally determined composition allow for creation of practical steady state conditions. This extends the range of materials that now can be crystallized in oxidizing, reducing, and neutral atmospheres and elevated pressure. Distribution of dopants is relatively uniform. The important problems of zone stabilization and its dependence on the conditions applied are discussed from the experimental point of view. Basic characterization of the grown crystals and most characteristic defects is presented. An extensive list of oxide crystals grown by the OFZ method is included. Floating zone crystal growth with radio frequency (RF) heating is an important technique for the preparation of single bulk crystals. The absence of any crucible is advantageous for the growth of single crystals of reactive materials with high melting points. The melt convection driven by the induction heating and the heat radiation from the surface leads usually to a solid–liquid interface being concave toward the solid phase outer rim. These concave parts inhibit the growth of single crystals over the whole cross-section. The concave solid–liquid interface can be prevented by a two-phase inductor that melts the material but also stirs it in a certain way. The basic design of this two-phase inductor is given, and its application for the growth of industrially relevant single crystals of RuAl and TiAl intermetallic compounds as well as interesting compounds for research such as antiferromagnetic Heusler MnSi compounds or biocompatible TiNb alloys is described.

Single-crystal diffuse scattering data have been collected at room temperature on synthetic titanite using both neutrons and high-energy x-rays. A simple ball-and-springs model reproduces the observed diffuse scattering well, confirming its origin to be primarily due to thermal motion of the atoms. Ab initio phonons are calculated using density-functional perturbation theory and are shown to reproduce the experimental diffuse scattering. The observed diffuse x-ray and neutron scattering patterns are consistent with a summation of mode frequencies and displacement eigenvectors associated with the entire phonon spectrum, rather than with a simple, short-range static displacement. A band gap is observed between 600 and 700 cm(-1) with only two modes crossing this region, both associated with antiferroelectric Ti-O motion along a. One of these modes (of Bu symmetry), displays a large LO-TO mode-splitting (562-701.4 cm(-1)) and has a dominant component coming from Ti-O bond-stretching and, thus, the mode-splitting is related to the polarizability of the Ti-O bonds along the chain direction. Similar mode-splitting is observed in piezo- and ferroelectric materials. The calculated phonon dispersion model may be of use to others in future to understand the phase transition at higher temperatures, as well as in the interpretation of measured phonon dispersion curves.

We respond to the comment of Bramwell et al (arXiv:1111.4168v1) to our original publication (S. R. Dunsiger et al, Phys. Rev. Lett. 107, 207207 (2011)), detailing muon spin rotation measurements of the Spin Ice compound Dy2Ti2O7.

Epitaxial films of Sr2RuO4 have been grown in situ by pulsed laser deposition on (100) LaAlO3 and (100) LaSrGaO4 substrates. X-ray diffraction results show that the films are single domain and grow c-axis oriented on (100) LaAlO3 and a-axis oriented on (100) LaSrGaO4 substrates. X-ray φ scans indicate epitaxial alignment of the film and substrate in-plane axes in both cases. Resistivity versus temperature measurements reveal that the as-grown c-axis oriented films are semiconducting and the a-axis oriented films are metallic.

Theory predicts the low temperature magnetic excitations in spin ices consist of deconfined magnetic charges, or monopoles. A recent transverse-field (TF) muon spin rotation (μSR) experiment [S. T. Bramwell et al., Nature (London) 461, 956 (2009)] reports results claiming to be consistent with the temperature and magnetic field dependence anticipated for monopole nucleation-the so-called second Wien effect. We demonstrate via a new series of μSR experiments in Dy(2)Ti(2)O(7) that such an effect is not observable in a TF μSR experiment. Rather, as found in many highly frustrated magnetic materials, we observe spin fluctuations which become temperature independent at low temperatures, behavior which dominates over any possible signature of thermally nucleated monopole excitations.

Poster Sessions C417 m/sec) and investigated for their hydrogen storage characteristics.The lower cooling rate obtained through low wheel speed (35 m/ sec) produces, i-phase grains whose size ranges from 300-350 nm.Whereas higher cooling rates obtained through high wheel speed (45 and 50 m/sec) promote the formation of nano-quasicrystalline grains with size ranges from 50-150 nm in Ti 45 Zr 38 Ni 17 ribbons.It has been found that the ribbons synthesized at 35 m/sec absorbed ~2.0 wt%, whereas ribbons synthesized at 50 m/sec absorbed ~2.84 wt.% of hydrogen.Thus the hydrogen storage capacity of ribbon increases with increasing quenching rate.One of the salient features of the present study is the improvement of hydrogen storage capacity obtained through higher quenching rates (~45 to 50 m/sec wheel speed) lead to the formation of lower grain size.

Magnetic measurements (ac and dc susceptibilities and magnetization) on YbCoGaO(4) single crystal as a function of frequency and temperature are presented. The studied system behaves like a three-dimensional Ising-like spin glass. A cusp is seen only in the longitudinal susceptibility, whereas a paramagnetic behavior is observed in the transverse susceptibility. Typical spin glass features are observed in the frequency and temperature dependence of the ac susceptibility. Dynamical scaling is performed and critical exponents are deduced and compared to those obtained for Ising and Heisenberg systems. The origin of the Ising anisotropy of Yb(3+) and Co(2+) ions is briefly discussed.

The (100) surface of MgAl2O4 is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg1/3Nb2/3O3(65%)–PbTiO3(35%). With a lattice mismatch of less than 0.5%, this film-substrate combination presents a geometrical template for growth that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties. From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material, but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that the (100) MgAl2O4 substrate could prove to be an effective substrate material, not only for the PbMg1/3Nb2/3O3(65%)–PbTiO3(35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice systems.

We report high resolution single crystal x-ray diffraction measurements of the frustrated pyrochlore magnet Tb2Ti2O7, collected using a novel low temperature pulsed magnet system. This instrument allows characterization of structural degrees of freedom to temperatures as low as 4.4 K, and in applied magnetic fields as large as 30 T. We show that Tb2Ti2O7 manifests intriguing structural effects under the application of magnetic fields, including strongly anisotropic giant magnetostriction, a restoration of perfect pyrochlore symmetry in low magnetic fields, and ultimately a structural phase transition in high magnetic fields. It is suggested that the magnetoelastic coupling thus revealed plays a significant role in the spin liquid physics of Tb2Ti2O7 at low temperatures.

Epitaxial (0 0 1)-oriented films of the metallic oxide (Ba 1− y Sr y )Ti 0.5 Nb 0.5 O 3 , with y =0, 0.4, 0.5 and 0.6, are deposited onto (0 0 1) MgAl 2 O 4 substrates using the pulsed laser deposition technique. The strontium for barium substitution gives rise to a decrease in the lattice constant, without altering the conductivity of the film. X-ray diffraction measurements show a significant number of [1 1 1], [0 1 1] and [2 2 1] misoriented grains that are not present for the y =0.6 composition. Transmission electron microscopy images of the film–substrate interface obtained for the y =0.6 composition show a sharp interface with flawless epitaxy. We attribute the improvements to a decrease in the lattice misfit strain made possible through the superior lattice match to the substrate obtained through strontium substitution.

Ba Ti 1 − x Nb x O 3 films, spanning the entire range of x, have been deposited on MgAl2O4 substrates. X-ray diffraction measurements indicate single phase films for all values of x, contrary to a previously reported niobium solubility limit. Films show extreme sensitivity to high temperature oxygen exposure, which destroys conductivity and severely disrupts crystallinity. Under optimum growth conditions increasing x gives rise to a Ti4+ to Ti3+ transformation in the oxidation state accompanied by increased conductivity with a semiconductor-metal transition near x=0.2. Temperature dependent magnetic measurements show an anomalous rise in the spin moment, a feature supportive of the small singlet bipolaron model.

The insulator/metal transition induced by hole doping due to neodymium vacancies of the Mott-Hubbard antiferromagnetic insulator, Nd1xTiO3, is studied over the composition range 0.0106x 0.24310. Insulating p-type conduction is found for x 0.07110. Anderson localization in the presence of a Mott-Hubbard gap is the dominant localization mechanism for the range of 0.07410x 0.0891 samples. For x 0.0891, n-type conduction is observed and the activation energy extrapolates to zero by x 0.1. The 0.0958x 0.20310 samples are Fermi-liquid metals and the effects of strong electronic correlations are evident near the metal-to-insulator boundaries in features such as large Fermi liquid T 2 coefficients. For 0.0749x 0.1124, a weak negative magnetoresistance is found below 15 K and it is attributed to the interaction of conduction electrons with Nd 3+ magnetic moments. Combining information from our companion study of the magnetic properties of a Nd1xTiO3 solid solution, a phase diagram is proposed. The main conclusions are that long-range antiferromagnetic order disappears before the onset of metallic behavior, and that the Anderson-Mott transition occurs over a finite range of doping levels. Our results differ from conclusions drawn from a similar study on the hole-doped Nd1xCaxTiO3 system, which found the coexistence of antiferromagnetic order and metallic behavior and that the Mott transition occurs at a discrete doping level.

YBa2Cu3O7-delta thin films are heavily microtwinned due to the crystal's orthorhombic unit cell and the confining effects of underlying substrate. Single crystal YBCO can be detwinned by thermally annealing the sample while applying uniaxial pressure. A similar technique has been devised to detwin a portion of a YBCO thin film. Through the use of photolithographic techniques, a suspended YBCO microbridge structure is fabricated, but with both ends of the bridge anchored to the substrate. During a subsequent anneal, the ends of the bridge induce a uniaxial stress along its length that arises from the lattice misfit and the thermal expansion coefficient mismatch between YBCO and the underlying materials. Without the confining effects of the substrate the suspended material can either detwin or twin on a macro length scale; the extent of which is largely determined by the substrate material. The ability to produce superconducting YBCO bridges that range from heavily microtwinned, to macrotwinned, to nearly detwinned provides an ideal experimental system. To study these phenomena. an optical and laser scanning microscopy set-up was employed. The images obtained provide insight into the role that twins play in determining the transport properties of superconducting YBCO thin films.

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films are heavily microtwinned due to the crystal's orthorhombic unit cell and the confining effects of underlying substrate. Single crystal YBCO can be detwinned by thermally annealing the sample while applying uniaxial pressure. A similar technique has been devised to detwin a portion of a YBCO thin film. Through the use of photolithographic techniques, a suspended YBCO microbridge structure is fabricated, but with both ends of the bridge anchored to the substrate. During a subsequent anneal, the ends of the bridge induce a uniaxial stress along its length that arises from the lattice misfit and the thermal expansion coefficient mismatch between YBCO and the underlying materials. Without the confining effects of the substrate the suspended material can either detwin or twin on a macro length scale; the extent of which is largely determined by the substrate material. The ability to produce superconducting YBCO bridges that range from heavily microtwinned, to macrotwinned, to nearly detwinned provides an ideal experimental system. To study these phenomena, an optical and laser scanning microscopy set-up was employed. The images obtained provide insight into the role that twins play in determining the transport properties of superconducting YBCO thin films.

Large, high-quality single crystals of (1−x)Pb(Zn1/3Nb2/3)–xPbTiO3 [PZN–PT] relaxors (with the composition range from ∼6 to ∼10% mol. PT) have been grown with a high degree of reproducibility by the gradient cooling method in a specially designed furnace from high-temperature solution. The crystal size is limited by the crucible diameter only. A preliminary series of more than 50 crystal growth experiments using the "standard" flux method allowed optimizing of the staring composition and temperature program. The segregation coefficient for Ti cations has been established on the basis of chemical analysis of the crystal composition and it was found that is strongly dependent on the Ti content in the melt. Samples cut from these crystals, after poling, have shown the expected high d33 values.

Single crystals of YBa2Cu3O7-δ (YBCO) have been detwinned under the simultaneous application of heat and uniaxial stress. This approach, however, has proved futile in thin films as they become heavily twinned due to strain from the underlying substrate as well as the orthorhombic unit cell. This lack of control over twinning has made it difficult to determine the role that twins play in determining the transport properties of films. Here, we present a technique for detwinning YBCO thin films. The detwinning in YBCO thin film is achieved by suspending a portion of the YBCO film above the underlying substrate. The suspended material is no longer influenced by the confining effects of the substrate and this allows it to detwin under the application of a uniaxial stress brought about by an anneal. With this technique, we are able to produce high-quality detwinned regions that will help aid the understanding of transport mechanisms in YBCO.

Magnetic flux jumps in textured Bi2Sr2CaCu2O8+delta have been studied by means of magnetization measurements in the temperature range between 1.95 K and T (c), in an external magnetic field up to 9 T. Flux jumps were found in the temperature range 1.95-6 K, with the external magnetic field parallel to the c axis of the investigated sample. The effect of sample history on magnetic flux jumping was studied and it was found to be well accounted for by the available theoretical models. The magnetic-field sweep rate strongly influences the flux jumping and this effect was interpreted in terms of the influence of both flux creep and the thermal environment of the sample. Strong flux creep was found in the temperature and magnetic-field range where flux jumps occur suggesting a relationship between the two. The heat exchange conditions between the sample and the experimental environment also influence the flux jumping behavior. Both these effects stabilize the sample against flux instabilities, and this stabilizing effect increases with decreasing magnetic-field sweep rate. Demagnetizing effects are also shown to have a significant influence on flux jumping.