Effect of Sr~(2+) doping on sintering behavior, microstructural development and electrical properties of LaPO_4·nH_2O nanorods prepared by dry mechanical milling

摘要

The effect of Sr2+ doping on the presence of second phases, sintering behavior, micro structural development, and electrical properties of LaPO4 center dot nH(2)O nanorods (La1-xSrxPO4-x/2 where x = 0.025 and 0.05) obtained by a dry mechanochemical milling process was investigated. When Sr2+ is present monazite-type La1-xSrxPO4 nanopowders were obtained instead of rhabdophane-type LaPO4 center dot nH(2)O. In addition, Sr2+ doping implies a larger P/La ratio and it enhances the formation of lanthanum tryoxophosphate (La(PO3)(3)), a thermodinamically stable phase, in doped samples. Dilatometric studies reveal a shift of the maximum shrinkage rate at lower temperatures for doped samples, with larger shifts with higher Sr2+ contents. This shift is related to the presence of oxygen vacancies but also to a higher content of La(PO3)(3). Furthermore, the derivative of the linear shrinkage curves for all the samples showed peaks at temperatures higher than 1300 degrees C that are associated to the volatilization of P4O10 gas and to the recrystallization of monazite from the incongruent melting of La(PO3)(3). After the dilatometric tests at 1500 degrees C the samples showed polygonal grains with a bimodal size distribution. For the doped samples the smaller grains do not present Sr2+ in their composition and it is related to those grains form from the recrystallization of monazite-LaPO4 formed in turn from La(PO3)(3). The total conductivity of the studied samples (x = 0.05) is higher for the samples sintered at 1000 degrees C for 1 h than for those sintered at 1500 degrees C without any dwell time. It can be due in part to the fact that the smaller grains of the samples sintered at 1500 degrees C do not contain Sr2+ and it can hinder the charge transport. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.