Co2+-Stuffed Quartz Solid Solutions With Zero Thermal Expansion Synthesized by Sol-Gel Spray-Drying

Abstract

Glassy nanobeads of nominal composition CoO·Al2O3·4SiO2, doped with some Li2O to foster their crystallization, were synthesized by spray-drying from a methanol-based solution. Heat treatments at 850 °C and 900 °C successfully induced the formation of quartz solid solution crystals, whose thermal expansion was found to be very close to zero between 25 °C and 625 °C (average linear coefficient of thermal expansion CTE = 0.3 x 10-6 K-1). Annealing at higher temperatures induced structural unstuffing of the solid solutions, accompanied by the parallel formation of CoAl2O4 spinel and by a color shift of the powders from purple to blue. Sol-gel spray-drying stands out as a highly versatile synthesis method that can harness the thermal expansion tunability of quartz solid solution phases within a (quasi) lithium-free compositional landscape.