Compositional variation in 0.65 PbMg2/3Nb1/3O3 ‐0.35 PbTiO3 single crystals grown by high temperature solution growth technique

Single crystals of lead magnesium niobate titanate, 0.65 PbMg_2/3Nb_1/3O₃ (PMN) ‐0.35PbTiO₃ (PT) were grown using flux method near morphotropic phase boundary (MPB) composition. The crystals grown at the centre of the platinum crucible were found to PT deficient compared to those grown near the walls of the crucibles. A variation of ∼3.8 mol% in PT concentration was found in the crystals grown at the wall and at the centre of the crucible. The difference in the chemical composition of crystals grown at the centre and the near the wall of the crucible was observed by X‐ray diffraction, EDXRF, dielectric and thermal measurements. The presence of PT rich and deficient crystals is explained in terms of the segregation coefficient of PT in PMN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of rhodium incorporation in KTiOPO4 single crystals grown from self‐flux

The presence of an impurity like rhodium in the platinum crucible used for the growth of KTiOPO₄ (KTP) single crystals can have severe consequences in the performance of devices made from these crystals. In the present study the effect of rhodium incorporation has been investigated. Rhodium‐incorporated KTP crystals have a lower ionic conductivity (1.3 × 10^–7 S/cm at 100 kHz) than pure KTP crystals (3.5 × 10^–6 S/cm at 100 kHz) along the c‐axis. And the optical absorption in the green‐wavelength regime leads to a detrimental effect on their SHG performance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bay Functionalized Perylenediimide with Pyridine Positional Isomers: NIR Absorption and Selective Colorimetric/Fluorescent Sensing of Fe<Superscript>3+</Superscript> and Al<Superscript>3+</Superscript> Ions

Bay functionalized perylene diimide substituted with pyridine isomers, (2-pyridine (2HMP-PDI), 3-pyridine (3-HMP-PDI) and 4-pyridine (4-HMP-PDI)) have been synthesized and explored for selective coloro/fluorimetric sensing of heavy transition metal ions. HMP-PDIs showed strong NIR absorption (760–765 nm) in DMF. The absorption and fluorescence of HMP-PDIs have been tuned by make use of pyridine isomers. Reddish-orange color was observed for 2-HMP-PDI (λ_max = 437, 551, 765 nm) whereas 4-HMP-PDI exhibited light green (λ_max = 432, 522, 765 nm). 3-HMP-PDI showed orange-yellow (λ_max = 431, 524, 762 nm). The fluorescence spectra of 2-, 3- and 4-HMP-PDI showed λ_max at 585, 538, 546 nm, respectively. Interestingly, HMP-PDI dyes showed selective color change (intense pink color) and fluorescence quenching for Fe³⁺ and Al³⁺ metal ions in DMF. Absorbance spectra revealed complete disappearance of NIR absorption and intensification/appearance of new peak at lower wavelength. The concentration dependent studies suggest that 4-HMP-PDI can detect up to 36.52 ppb of Fe³⁺ and 43.12 ppb of Al³⁺ colorimetrically. The interference studies in presence of other metal ions confirmed the good selectivity for Fe³⁺ and Al³⁺. The mechanistic studies indicate that Lewis acidic character of Fe³⁺ and Al³⁺ ions were responsible for selective color change and fluorescence quenching.     

Two new oligostilbenes with dihydrobenzofuran from the stem bark of Vateria indica

Two new stilbenoids, vateriaphenols A (1) and B (2), were isolated from the stem bark of Vateria indica along with known 10 stilbenoids (3-12) and bergenin (13). The structures of isolates were established based on spectroscopic analysis. The structures of vateriaphenols A and B were characterized as an octamer and a tetramer of resveratrol, respectively. The spectral properties of the highly condensed vateriaphenol A were also discussed.     

Growth kinetics of zinc(tris)thiourea sulphate (ZTS) crystals

Growth kinetics of zinc (tris) thiourea sulphate (ZTS) crystals investigated as a function of supersaturation is reported in this communication. Crystal growth rates were investigated normal to the (100), (010) and (001) faces under growth conditions employed for bulk crystal growth. The growth rates normal to (010) and (100) were found to follow the continuous growth model (R_G = Cσ) with respect to the supersaturation whereas the growth rates normal to (001) was found to satisfy birth and spread (B+S) model (R_G = Aσ^5/6 exp(‐B/σ)). The growth rates observed normal to the studied face are in agreement with the growth mechanism predicted from the estimated α (Jackson) factor. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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

Domain 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)