R. Kamel

Comparitive study of structure changes with temperature in univalent and divalent ionic nitrate crystals

Abstract The temperature dependence of the d.c. resistivity and dielectric constant of polycrystalline samples of Pb(NO 3 ) 2 , Ba(NO 3 ) 2 and Sr(NO 3 ) 2 were found to show anomalies in the high temperature region. In addition, sharp peaks were obtained in both differential thermal analysis (DTA) and thermomechanical analysis (TMA) curves in the same temperature range. The observed anomalies were attributed to orientational disorder of the nitrate group leading to an order-disorder phase transition which is reported here for the first time. A comparison is made between the role of NO 3 − ions in both the divalent and univalent nitrates, taking NaNO 3 as representative. The TMA curve for Sr(NO 3 ) 2 showed a pronounced peak at 325°C. This peak was related to a sudden increase in the expansion coefficient associated with the rotation of the NO 3 − group leading to a solid state phase transformation. Energy diagrams describing the conduction mechanism and showing a fractionization of energy barriers in the case of divalent nitrates are introduced.

The effect of impurity content on magneto-mechanical interaction in Ni-5 wt.% Mn

Abstract The initial magnetic permeability was used to study the magneto-mechanical interaction of dislocations with migrating domain walls under low magnetic fields in pure nickel and Ni-5 wt.% Mn. The observed stress sensitivity of initial permeability, μi, was inferred to be of a magnetic as well as an elastic origin. The decrease of μi with stress was attributed magnetically to rearrangements in domain structure involving the vanishing of 180°-walls. Elastically, it was suggested that a network of structural defects existed producing a configuration of potential energy controlling the location of magnetic domains. The existence of the Mn-solute atoms in Ni-5 wt.% Mn extended the region of stress sensitivity, of initial permeability, observed in pure Ni, to higher stress ranges.