Phase transitions in superionic PbSnF₄

PbSnF\sb4 is the highest performance fluoride ion conductor known to date. We have studied the phase transitions it undergoes under three different conditions: (i) versus the amount of hydrofluoric acid used for the preparation by the aqueous route, (ii) upon application of mechanical energy, and (iii) versus temperature. The addition of an aqueous solution of lead(II) nitrate to a fresh aqueous solution of SnF\sb2 results in the precipitation of $\alpha$-PbSnF\rm\sb4(aq\sb1), which is very highly strained in the ($\vec a,\vec b$) plane of the tetragonal unit-cell. If a very minor amount of hydrofluoric acid is used, the strain increases and o-PbSnF\sb4 is obtained. The $\alpha$-PbSnF\sb4\to o-\rm PbSnF\sb4 transition is mostly a bidimensional phase transition, which includes a highly disordered intermediate "transitional phase". Ball milling results in a phase transition, giving microcrystalline disordered $\mu\gamma$-PbSnF\sb4, a cubic $\beta$-PbF\sb2 like phase. Tests were performed to make sure the $\mu\gamma$-PbSnF\sb4 samples are indeed microcrystalline cubic PbSnF\sb4 and not a mixture of microcrystalline $\beta$-PbF\sb2 and amorphous SnF\sb2. Milling $\alpha$- and $\beta$-PbF\sb2 for comparison and testing showed that both $\beta\to\alpha$ and $\alpha\to\beta$ transitions take place upon milling. Stirring $\alpha$-PbF\sb2 in an aqueous solution of SnF\sb2 results in the formation of $\rm\alpha$-PbSnF\rm\sb4(aq\sb2) or \rm Pb\sb2SnF\sb6 depending on the conditions whereas no reaction occurs with $\beta$-PbF\sb2. When all the phases of PbSnF\sb4 are heated, phase changes take place versus temperature and time. Our findings provide key knowledge that will have to be taken into account in the fabrication of practical devices using PbSnF\sb4 for guaranteed reproducible results, long term stability and stable output of the device

Consumer Preferences for Purple Yam (Dioscorea alata L.) Powder Brands: Implications for a Product Developed by the University of the Philippines Los Baños

The study compares the attributes of three brands of purple yam (Dioscorea alata L.) powder, namely, Giron Powdered Purple Yam, FST Foods Purple Yam “Ubi” Powder, and Bohol’s Tru Ubi Powder, and the resulting ubi halaya, a local pudding made of purple yam, made from these brands. Store checks, focus group discussions (FGDs), product and home placement tests, and a consumer survey for the local market were used as data-gathering tools. Frequency counts, mean ratings, and standard deviation were used to analyze consumer awareness, consumption behavior, and product attribute importance ratings of respondents. Kruskal-Wallis test was also employed to find out if there were significant differences in the mean ratings for all attributes across brands. The results of the study show that consumers preferred the attributes of the FST Foods Purple Yam “Ubi” Powder and the halaya made using the brand. The product can thus be considered ready for commercialization by potential investors. However, it is recommended that a detailed set of product use instructions should be printed in its packaging to come up with halaya that has better taste, aroma, and consistency.