St Petersburg University crystallographers find a way to improve the quality of feldspar—based ceramics

Feldspars are the most common minerals in the Earth’s crust. BaAl2Si2O8 (barium feldspar-based minerals) and their synthetic analogues are widely used in industry due to their low thermal expansion, high melting temperature, chemical resistance, and attractive luminescence properties.

The project is supported by a grant from the Russian Science Foundation. The research findings are published in the Journal of the European Ceramic Society.

According to Liudmila Gorelova, the corresponding author of the article, Associate Professor in the Department of Crystallography at St Petersburg University, materials based on BaAl2Si2O8 gradually degrade and break down during operation due to a large number of phase transitions. Although these materials are widely used, the crystal structures of their high-temperature modifications have not been studied yet. 

It is essential to know how and why minerals are destroyed and to find ways to improve the quality and durability of various ceramic materials based on BaAl2Si2O8. Almost 70 years of research have accumulated inconsistent data on this topic. The up-to-date infrastructure and high-tech equipment at the St Petersburg University Research Park allowed the University scientists for the first time to reliably determine the crystal structures of all high-temperature modifications of barium feldspars and trace the paths of their transformation.

The durability of materials, primarily ceramics, based on barium feldspar strongly depends on phase transitions between low- and high-temperature modifications. In our project, we used a complex of modern research methods, such as in-situ high-temperature single-crystal X-ray diffraction (SCXRD), and micro-Raman spectroscopy up to 1000 °C.

Liudmila Gorelova, the first author of the article, Associate Professor in the Department of Crystallography at St Petersburg University

St Petersburg University found out that the crystal structure of ‘α-hexacelsian’, i.e. a high-temperature modification of BaAl2Si2O8, under ambient conditions is monoclinic, that is, low-symmetric. The alpha-form undergoes two polymorphic transformations upon heating, that is accompanied by an increase in symmetry. These transitions lead to significant changes in the unit-cell volume. 

The University’s scientific group of crystallographers is planning to continue studying other members of the feldspar family under extreme conditions, since gaining a deeper insight into the structural transformations will allow them to better understand the mechanisms of destruction of ceramic materials and select optimal temperatures for ceramics production and ways of ceramic annealing. 

"We hope that in addition to solving the fundamental crystal chemical problems we will be able to provide answers to applied questions so that our research will help in the development and improvement of new materials based on feldspar," said Liudmila Gorelova.

In 2024, the Department of Crystallography at St Petersburg University marks its 100th anniversary. The department is widely known in Russia and abroad for its scientific traditions and discoveries.

The study of barium feldspars continues the work in the field of high-temperature crystallography, initiated by St Petersburg University Professor Stanislav Filatov. Over the years of his activity at St Petersburg University, he extensively studied minerals and mineral-like materials using powder diffraction methods. 

The project of the scientific team under the leadership of Liudmila Gorelova is supported by a grant No 22-77-10033 from the Russian Science Foundation. The research was carried out at the Research Park at St Petersburg University: Centre for Optical and Laser Materials Research; Centre for X-ray Diffraction Methods; Centre for Geo-Environmental Research and Modelling (GEOMODEL); and Computing Centre.