Electron and light microscopy studies on the domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I ferroic boracites
The domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I boracite single crystals were studied by means of polarized light in conjunction with electron microscopy. Single crystals of the three compositions were grown by chemical transport reactions in closed quartz ampoules, at a temperature of 900 °C and were examined by polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For both PLM and SEM, the same as‐grown samples were used without having to resort to metallization of the crystal faces. For TEM the single crystals were crushed and mounted on holey carbon films. Comparative electron microscope images were useful for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of an optical microscope. X‐ray diffraction analysis of the pulverized crystals was performed for this triad of halogen boracites containing zinc as a common metal.
New facile method for the preparation of M3B7O13I boracites (M = Mn, Fe, Co, Ni, Cd).
Five iodine boracites, M(3)B(7)O(13)I (M = Mn, Fe, Co, Ni, Cd), have been synthesized by reactions of metal oxide, B(2)O(3), element B, and I(2) at intermediate temperature above 350 °C. Powder X-ray diffraction analyses verify the identities and purity of the products, which are also confirmed by magnetic property measurement. Except safe, cheap, and convenient, this novel method is significantly flexible in the selection of the starting metal oxide. The influence of the reaction temperature and time has also been studied.
Heat of Formation and Entropy of (BOCl)3
An experimental study of the equilibrium B2O3(l)+BCl3(g) = (BOCl)3(g) has been made by the method of transpiration in the temperature range of 536°—825°K. The enthalpy and entropy changes of the reaction in this temperature range were found to be 5.0±0.3 kcal/mole and 3.1±0.5 cal/deg/mole, respectively. The data have been interpreted to yield the heat of formation, ΔH°f695°K = 391.5±0.3 kcal/mole, and entropy, S°695°K = 124.2±0.5 cal/deg/mole, of gaseous (BOCl)3. Partial pressure studies indicate that the quantity of the monomer, BOCl, present in the temperature range under consideration is negligible.