Synthesis and in situ transformation of PST-1: a potassium gallosilicatenatrolite with a high Ga content

摘要

The synthetic details of a novel potassium gallosilicate natrolite with Si/Ga = 1.28, denoted PST-1, aredescribed. The presence of K~+ and Ga with well-defined levels of concentration in the synthesis mixtureis essential for directing its crystallisation. PST-1 transforms rapidly into TNU-6 under hydrothermalconditions, behaviour that contrasts sharply with its very high thermal and hydrothermal stability,which is unusual for a material of such a high Ga content. These stability issues are discussed andrationalized based on chemical composition, likely violations of Loewenstein's rule and the temperatureof dehydration of as-made K-PST-1. The crystal structure of TN U-6 has been resolved through thecombined use of synchrotron X-ray and electron diffraction data; it has the BaFeGaO4 structure typewith an additional 3~(1/2)a x 3~(1/2)a "GeA1O_4" superstructure that arises from tilting of some of thetetrahedral units in all of the 6-rings.