Cut Single Crystals Research Articles

Formation of single domain state and spontaneous backswitching in SBN single crystal

ABSTRACTFormation of the single domain state and spontaneous backswitching have been studied in polar cut single crystals of relaxor ferroelectric strontium-barium niobate SrxBa1-xNb2O6 with x = 0.61. The piezoresponse force microscopy has been used for domain visualization. Two methods of creation of the single domain state were applied: (1) cyclic switching below freezing temperature and (2) cooling from the temperature corresponding to relaxor phase to room temperature in constant field. The domain structure, appearing as a result of spontaneous backswitching after fast removal of the external field, have been revealed and analyzed.

High magnetic-field scales and critical currents in SmFeAs(O, F) crystals

Superconducting technology provides most sensitive field detectors, promising implementations of qubits and high field magnets for medical imaging and for most powerful particle accelerators. Thus, with the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications rather difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. While many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clarified. Thus we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of optimally doped SmFeAs(O,F) single crystals reveals a promising combination of high (>2 x 10^6 A/cm^2) and nearly isotropic critical current densities along all crystal directions. This favorable intragrain current transport in SmFeAs(O,F), which shows the highest Tc of 54 K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are 4-probe measurements on Focused Ion Beam (FIB) cut single crystals with sub-\mu\m^2 cross-section, with current along and perpendicular to the crystallographic c-axis and very good signal-to-noise ratio (SNR) in pulsed magnetic fields. The pinning forces have been characterized by scaling the magnetically measured "peak effect".

Gain in spatial resolution of X-ray laboratory microtomographs with enlarging X-ray optical elements

Two types of x-ray optical elements are discussed – capillary air bubble lens and asymmetric cut single crystal. These elements are applied to laboratory microtomography. Several reconstructions using laboratory x-ray source (2 kW, 1×1 mm2 size) and the optical elements are obtained. Best voxel size of 1 μm is achieved using two crossed asymmetric cut single crystal (Bragg magnifier) and 14×14 μm pixel CCD camera. Two times magnifying x-ray microtomograph with 7.5 μm resolution was built using capillary air bubble lens.

Domain structure and birefringence studies on a 0.91Pb(Zn1/3Nb2/3)O3 ‐0.09PbTiO3 single crystal

AbstractDomain structure and phase transition sequence of 0.91PZN‐0.09PT single crystal, grown from high temperature solution, have been analysed using polarised light microscopy. The domain structure of (001)cub cut single crystal exhibit co‐existence of rhombohedral and tetragonal phases. The sequence and phase transition temperatures have been determined from temperature dependence of birefringence. Birefringence measurements during heating and cooling reveal a first order nature of phase transition between rhombohedral (R3m) and tetragonal (P4mm). The birefringence was measured with accuracy of 10‐3. However, dielectric measurement does not provide any evidence of R3m ‐ P4mm phase transition. It is shown that in‐situ analysis of domain structure and phase transition can be used as non‐destructive analytical tool for determination of local composition and phase transition sequence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Satterlyite, (Fe,Mg)12(PO3OH)(PO4)5(OH,O)6: crystal structure and infrared absorption spectra

The crystal structure of satterlyite from the Big Fish River area, Yukon Territory, Canada, (Fe 0.77 Mg 0.23 ) 12 (PO 3 OH)(PO 4 ) 5 (OH,O) 6 (space group P 31 m , a = 11.355(1), c = 5.0394(5) A, V = 562.71(9) A 3 , Z = 1), has been solved and refined using single-crystal intensity data (Mo K α X-radiation, CCD area detector, 2320 unique reflections with F 0 > 4σ( F 0 ), Rl = 2.15 %). The structure is based upon pairs of face-sharing, distorted (Fe,Mg)O 6 octahedra linked by edge-sharing to form double chains along [001]. Each double chain shares ligands with six other double chains to produce a three-dimensional network hosting three unique PO 4 tetrahedra which are corner-linked to the (Fe,Mg)O 6 octahedra. The two unique (Fe,Mg)O 6 octahedra are characterised by different occupancies; Fe:Mg ratios of the M (1) and M (2) sites are 0.838(2):0.162(2) and 0.706(2):0.294(2), respectively. Two H atoms are each bonded to common ligands of the two (Fe,Mg)O 6 octahedra. The third, strongly disordered H(3) atom is bonded to the apical O of the P(l)O 4 tetrahedron. The H(3) site and possibly both the other two H sites are only partially occupied, and only very weak hydrogen bonds exist. Satterlyite is isostructural with holtedahlite, Mg 12 (PO 3 OH,CO 3 )(PO 4 ) 5 (OH,O) 6 . Unlike in natural holtedahlite, there is no carbonate-for-phosphate substitution in the satterlyite investigated, which was also confirmed by IR absorption powder spectra. A structural relationship exists with phosphoellenbergerite, Mg 14 (PO 4 ) 6 (PO 3 OH) 2 (OH) 6 . Polarised IR spectra of oriented cut single crystals in the O-H stretching vibrational range revealed an asymmetric band at 3536 cm -1 (including a weak shoulder at ∼ 3568 cm -1 ) and an asymmetric band at ∼ 3471 cm -1 . The number of hydroxyl vibrational bands and their positions are in accordance with the results of the structure refinement.

Resolution of the USANS diffractometer at the FRJ-2 research reactor in Jülich

The resolution of a Bonse–Hart setup with two Si(1 1 1) perfect channel cut single crystals is studied. The dimension of the crystals is determined in such a way as to avoid single reflected neutrons to leave the channels. The setup gives the same contrast ratio as the Oak Ridge instrument using a Cd absorber in the longer wall of the crystals. The applicability of the equipment is tested by the measurement of a monodisperse polystyrene latex dispersion model system.

Angular dependence of the upper critical field of the heavy fermion superconductor UPt3.

The angular dependence of the upper critical field ${H}_{c2}$ of ${\mathrm{UPt}}_{3}$ in magnetic fields up to 0.85 T has been measured. In spark cut single crystals a sixfold modulation of the resistivity is observed at the superconducting transition in the basal plane. This modulation vanishes as the temperature approaches ${T}^{*}$ temperature of the discontinuity in slope of the ${H}_{c2}$ ($T$)] and reappears for $T<{T}^{*}$ but with opposite sign. The results provide important new evidence on the nature of the change in the superconducting order parameter at ${T}^{*}$ and its possible coupling with the antiferromagnetism.

A monolithic X-ray monochromator with fixed exit beam position

To avoid the inconvenient lateral movement of the monochromated beam in conventional, monolithic monochromators while the wavelength is changed, a new approach has been made. In principle the device is a channel cut single crystal where the walls of the groove are curved in such a way that the parallel displacement between the incoming and outgoing beams is independent of the wavelength. The analytical description of the shape of the mirrors is derived and different designs are discussed. Restrictions due to the asymmetric reflections are pointed out. The influence of deviations from the exact geometry are investigated as well as the consequences of misalignments with respect to the primary beam. Finally the successful fabrication with support by the CANON company and the first operation in the beam of the Photon Factory are reported. The result of an EXAFS experiment using this monochromator is presented.