Crystal Growth of Some Rare Earth Molybdates by Gel Diffusion Technique

Holmium molybdate and gadolnium molybdate crystal were grown via a very simple and inexpensive gel diffusion technique. The effect of various factors such as gel age, growth period, temperature, gel pH, concentration of lower reactant and concentration of upper reactant on the crystallization process were investigated. As-grown samples were characterized by polarizing optical microscope, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Energy- Dispersive Analysis of X-rays (EDAX), Thermal methods (TGA, DTA). The powder X-ray diffraction (pxrd) results revealed these samples are of crystalline nature and the EDAX results provided their elemental composition. The pxrd studies revealed that the structure of both the laboratorygrown holmium molybdate and gadolnium molybdate crystals is triclinic belonging to the space group of P1 with a = 7.80 ˚A, b = 9.01 ˚A, c = 13.54 ˚A, α = 76.390, β = 131.380 and γ = 76.730; a = 7.1560 ˚A, b = 10.1980 ˚A, c = 10.1740 ˚A, α = 48.1400, β = 58.2200 and γ = 44.8400 as cell parameters respectively. The optical images showed them to be of spherulitic form and the SEM results revealed them to be composed of nano-crystallites. Holmium molybdate spherulites grown at room temperature are composed of nano-plates and those grown at a temperature of 45 ◦C are composed of nano-rods. Gadolnium molybdate spherulites were grown only at 45 ◦C and were also composed of nano-rods. The thermal analysis curves provided their thermal decomposition behaviour and revealed that the holmium molybdate and gadolnium molybdate crystals shows an isomorphic phase transion at 520 ◦C

Studies on crystal growth of some pure and mixed rare-earth Fumarates and their characteristics.

Crystal growth and its characterization has become valuable branch of science due to the growing demand of scientifically and technologically important crystals for different applications. Rare-earth based crystals of metal organic coordination compounds have an important role from both academic and technological point of view due to their outstanding physical, magnetic and luminescent properties. The compounds of rare-earths have also gained importance for their dielectric, ferroelectric, ferroelastic and conductivity behaviour. Due to the large applicability of rare-earth coordination compounds, it was thought worthwhile to investigate growth and characterization of tebium fumarate, gadolinium fumarate and mixed gadolinium-terbium fumarate heptahydrate single crystals for scientific investigations. The work presented in this thesis was carried out at the Solid-State Research Laboratory, Department of Physics, University of Kashmir, Srinagar. The thesis entitled “Studies on crystal growth of some pure and mixed rare-earth fumarates and their characteristics” is a comprehensive report on the growth of single crystals of terbium, gadolinium and mixed gadolinium-terbium fumarate heptahydrates in hydro silica gel and their detailed characterization. It also includes the results of dielectric, ac conductivity, thermal, luminescent and magnetic moment measurements of the grown crystals. The thesis is divided into two sections, Section-A pertaining to growth and characterization of crystals, consists of four chapters and section-B including the physical properties of as-grown crystals consists of five chapters.Digital copy of Thesis.University of Kashmir