Effect of Anion Impurity on Preparing Xonotlite Whiskers via Hydrothermal Synthesis

Effect of anion impurity on preparing xonotlite whiskers via hydrothermal synthesis was researched in this paper. The crystal phase composition and morphology of the xonotlite whiskers were analyzed using XRD and techniques. The results indicate that different anion impurity have little effect on the crystal phase composition of synthesized the products, but have great impact on the crystallinity and morphology of xonotlite whiskers. Xonotlite whiskers with well crystal and aspect ratio of 50-100 were successfully prepared from CaCl2 as calcium sources under the condition of 225 °C for 15 h with the reactant concentration of 0.05mol•L-1, but the hydrothermal process condition should be controlled at 225 °C for 40 h while using Ca(NO3)2 or Ca(OH)2 as calcium sources. Cl- iron can accelerate the process of hydrothermal synthesis and be beneficial to the crystallization of xonotlite in CaO-SiO2-H2O system.

NQR Investigation of Anion Dynamics in Rb2Zn(Cl1 - xBrx)4

The structural stability of Rb2Zn(Cl1 - xBrx)4 (x = 1% and 3%) is investigated using the 35Cl quadrupole resonance frequency and spin lattice relaxation time (T1Q) in the paraelectric (PE) phase. The PE to incommensurate (IC) phase transition temperature T1, observed at 302 K in the pure compound, is lowered to 300 K for x = 1 % and to 293 K for x = 3%. These effects are smaller than in the earlier reported case of 3% Cs substitution in Rb2ZnCl4 , which reduces T1 by 25 K. While bigger cation substitution affects only the barrier for anion dynamics about directions perpendicular to the a-axis (direction of low temperature IC modulation wave), bigger anion substitution is found to affect the barrier for anion dynamics about the a-axis as well. The present study also indicates that the cusp like dip in T1Q observed while approaching T1 from above (characterizing the soft mode condensation associated with the structural phase transition) is essentially unaffected by anion impurity substitution, in contrast to the case where bigger cation substitution tends to smear the transitional effects. These results seem to suggest the dominant role played by cations in stabilizing the PE phase of these A2BX4 systems, in comparison to anions.