Xiaobai Wang

Raman scattering investigations of the antiferroelectric–ferroelectric phase transition of NaNbO3

The antiferroelectric to ferroelectric phase transition in NaNbO3 was investigated by Raman scattering between 295 and 10 K. The transition occurs at 185 K on cooling and the antiferroelectric and ferroelectric phases coexist at low temperature. The transition occurs at 210 K on heating and the relatively large hysteresis is attributed to the difficulty in reversing the spontaneous polarization direction at the transition. The results agree well with low-temperature x-ray data which show that both phases coexist if the crystal samples are twinned. The transition is not considered to be of the displacive type, although two modes at 115 and 121 cm-1 were observed to soften at low temperature.

High temperature Raman study of phase transitions in antiferroelectric NaNbO3

Abstract The Raman spectra of antiferroelectric NaNbO3 have been studied at temperatures up to 480°C. Two phase transitions were observed, one at 376°C in consistence with the previous observations, and the other being a new phase transition at 190°C. There is no evident hysteresis for this transition, which indicates that the phase transition is of second order.

Substrate temperature dependence of the texture quality in YBCO thin films fabricated by on-axis pulsed-laser ablation

In applications of superconducting devices, the crystalline texture of high-quality thin films is of primary importance. The preferred orientation of the films can be essentially controlled by means of the substrate temperature, . In order to study the dependence of the film texture on different , a series of films were deposited on YSZ substrates by the on-axis pulsed-laser ablation technique. The substrate temperature was varied from to while the rest of the growth parameters remained the same. Various analytical techniques, including x-ray diffraction, scanning electron microscopy, micro-Raman spectroscopy and the four-point probe method, were applied to characterize the films. At around , the best films with the smoothest surface morphology, lowest FWHM of the rocking curve and highest in-plane texture were obtained. The resultant in excess of at 77 K and around 91 K were also achieved at this temperature.

Self-assembly of a 1D helical coordination polymeric lead(II) complex with Pb ¿ O(perchlorate) ¿ Pb scaffoldings

Abstract The structure of a Pb(II) complex of a tridentate ligand namely, N-(2-pyridylmethyl)- l -alanine (Hpala) has been found to have single stranded helical structure, pillared by Pb⋯O⋯Pb interactions from ClO4 anions.

Preparation, characterisation and structures of copper(II) complexes of an asymmetric anti-cancer drug analogue†

A series of copper(II) complexes of the anti-cancer drug analogue 1,5-bis(2-pyridylmethylene)thiocarbonohydrazide (H2L) was synthesized from acid solution. The single crystal structures of two asymmetric, binuclear, complexes [{Cu2(HL)(H2PO4)2}2][NO3]2·2H2O and [{Cu2(HL)(CF3CO2)3}2] and two mononuclear, monomeric complexes [Cu(H3L)(H2O)][ClO4]3·2H2O and [Cu(H3L)(NO3)2]NO3 were solved. The binuclear complexes are dimeric with three-atom anion bridges. Selective removal of one copper ion gives mononuclear monomers. The primary magnetic exchange is between copper(II) centres within a planar binuclear unit with weaker interactions via anion or sulfur bridges.

Structure and magnetic properties of a neutral dimeric copper (II) complex of N-(2-hydroxybenzyl)glycinamide ligand

A copper (II) complex ([Cu2(sglym)2(NO3)2]) of tridentate reduced Schiff base ligands, namely, (N-(2-hydroxybenzyl)-glycinamide (Hsglym) was synthesized and characterized in the solid state by single crystal x-ray diffraction techniques. The two Cu(II) atoms are bridged by two phenolate oxygen atoms in the neutral dimers and the geometry of Cu(II) can be described as a distorted square pyramid. The Cu–Cu distances are 3.020(2) A. The magnetic properties of the complex were studied at variable temperatures. Transition of spin state (from spin zero to spin one) was observed due to thermal excitation. This transition of spin state observed in the temperature range 100–400 K was accompanied by magnetic viscosity.

Structural and magnetic properties of an asymmetric dicopper(II) anticancer drug analogue

The single-crystal X-ray structure and variable temperature magnetic properties of the novel dicopper(II) anticancer drug analogue [{Cu2(HL)(H2PO4)2}2][NO3]2·2H2O [H2L = bis(pyridine-2-aldehyde) thiocarbohydrazone] is determined; the complex shows a dimer of dimeric {Cu2(HL)}3+ units with dihydrogenphosphato and sulfur bridges between the inequivalent CuII centres, resulting in three antiferromagnetic exchange interactions: a dominant intradimer J of –109 to –116 cm–1, and two weaker interdimer interactions.