α-Nickel sulfate hexahydrate crystals: relationship of growth conditions, crystal structure and properties

Studies on α-nickel sulfate hexahydrate (NSH) crystals grown under different conditions are undertaken to investigate how changes in growth conditions affect crystal properties and whether or not there is any modification of the average crystal structure due to changes in crystallization conditions. Thermogravimetric and microhardness studies were carried out on the crystals grown from two different aqueous solutions, one of them containing an excess of sulfuric acid. Raman spectra were recorded and a single-crystal neutron diffraction investigation was conducted on both crystals. A detailed comparison between the two crystal structures and their Raman spectra showed that, although the two crystal structures are very similar, there are slight differences, such as the change in unit-cell volume, differences in the ionic structure, particularly of the sulfate ions, and changes in the hydrogen-bonding network. During solution crystal growth of a salt like NSH, varying the ionic environment around the solute ions influences the interionic interactions between them. Hence it is suggested that the above-mentioned structural differences result from a fine-tuning of the interionic interaction between the cations and anions of NSH in the solution phase. This difference is finally carried over to the crystalline phase. The resulting small crystal structure differences are enough to produce measurable changes in the thermal stability and fragility of the crystals. These differences in crystal properties can be explained on the basis of the observed structural differences between the two crystals grown under different conditions.

Study of Energy of Formation for FexNi1-x Liquid Binary Alloys

In this present study we have systematically calculated the free energy of formation for FexNi1-x binary alloys at a thermodynamic state T = 1920 K. A microscopic theory bases on first order perturbation theory along with a reference hard sphere liquid has been applied. The interionic interaction is described by Bretonnet-Silbert local pseudopotential that capable of takes into account the s-d hybridization in electro-ion interaction in transition metals. The effective hard sphere diameters have been determined using linearized Weeks-Chandler-Andersen (LWCA) perturbation theory and the partial structure calculated in line with Ashcroft and Langreths original work. The calculated theoretical value and available experimental data for free energy of formation are in agreement quite satisfactorily.

Theoretical Analysis of the Structural Phase Transformation and Elastic Properties in the ZrN under High Pressure

We report a phenomenological model based calculation of pressure-induced structural phase transition and elastic properties of ZrN compound. Gibb’s free energy is obtained as a function of pressure by applying an effective interionic interaction potential, which includes the long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach. From the present study, we predict a structural phase transition from NaCl structure (B1) to the CsCl structure (B2). The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of NaCl type structure family.

Study of Structural, Elastic Properties and their Pressure Dependence in IrN Compound

A theoretical study of the elastic behavior in IrN compound using effective interionic interaction potential is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zinc blende (B3) to CsCl structure (B2). C11, C12 and C44 increase nearly linearly with pressure. At phase transition pressure IrN has shown a discontinuity in second order elastic constants, which is in accordance with the first-order character of the phase transition.