Growth of tourmaline single crystals containing transition metal elements in hydrothermal solutions

Abstract

Interest in the growth of tourmaline single crystals is based on the promising piezoelectric and pyroelectric properties of this material compared to quartz crystals currently in use. Moreover, synthetic tourmaline can be used as a substitute for the natural stone in the jewelry industry similar to other synthetic analogues of gemstones. Single crystals of colored Co-, Ni-, Fe-, (Ni,Cr)-, (Ni,Fe)-, and (Co,Ni,Cr)-containing tourmalines with concentration of transition metal elements up to 16wt% on a seed have been grown from complex boron-containing hydrothermal solutions at a range of temperatures 400–750°C and pressures 100MPa. Experiments were conducted under conditions of a thermal gradient in titanium and chromium–nickel autoclaves. Tourmaline growth on a seed crystal occurs only if separate tourmaline-forming components (monocrystalline corundum and quartz bars) are used as charge. All tourmalines specified above grow in analogous (+) direction of the optical axis with a speed of 0.05mm/day by faces of the trigonal pyramid, except tourmalines containing chromium. They grow in analogous (+0001) direction with a speed 0.05mm/day, and in antilogous (−0001) direction with a speed of 0.01mm/day by faces of the trigonal pyramid and in prism direction with a speed of 0.001mm/day. Along with the large single crystals, a great amount of finest (30–150μm in size) tourmaline crystals was formed during the runs by spontaneous nucleation both on the surface of the seed crystals and in the charge.