Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2

We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure conditions and analyzed the microstructure and pinning properties. The lattice constants and the Laue pattern of the crystals from X-ray micro-diffraction showed the crystal symmetry of MgB2. A thorough crystallographic mapping within a single crystal showed that the edge and c-axis of hexagonal-disc shape exactly matched the (10-10) and the (0001) directions of the MgB2 phase. Thus, these well-shaped single crystals may be the best candidates for studying the direction dependences of the physical properties. The magnetization curve and the magnetic hysteresis for these single crystals showed the existence of a wide reversible region and weak pinning properties, which supported our single crystals being very clean.Comment: 5 pages, 3 figures. submitted to Phys. Rev.

Acoustic characteristics of FeSe single crystals Acoustic characteristics of FeSe single crystals

The results of the comprehensive ultrasonic research of high quality single crystals of FeSe are presented. Absolute values of sound velocities and their temperature dependences were measured; elastic constants and Debye temperature were calculated. The elastic C11-C12 and C11 constants undergo significant softening under the structural tetra-ortho transformation. The significant influence of the superconducting transition on the velocity and attenuation of sound was revealed and the value of the superconducting energy gap was estimated.Comment: 5 pages, 7 figures, 1 tabl

Crystal growth of the cuprate superconductor La1.6-xNd0.4SrxCuO4 by the traveling solvent floating zone method

In this thesis, my efforts of the single crystal growth of a cuprate series La₁.₆₋[subscript x]Nd₀.₄Sr[subscript x]CuO₄ by the travelling solvent floating zone method will be described. The availability of high quality single crystals is essential to facilitate experimental studies of high temperature superconductivity in the cuprates. Repeated attempts gradually lead to crystals with the improved qualities. A single pattern well indexed via the X-ray powder diffraction suggests that the crystals were grown with the correct chemistry and single phase. Laue back reflection, on the other hand, indicates that domains with different orientations in the same crystals still exist, and crystal growth processes can be further optimized. Discussions, and possible routes of further optimization of the growth process are suggested at the end of the thesis based on the principles of the travelling solvent growth. A continuous supply of large and better quality crystals would help offer more insight into this challenging strongly correlated system.Physic

A preliminary review of organic materials single crystal growth by the Czochralski technique

The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed