Features of copper chloride nanocrystals formation in potassium aluminoborate glass

- CuCl nanocrystals with wurtzite type lattice inside the borate glass are revealed.
- β-CuCl phase precipitates in glass at the lower heat treatment temperatures than γ-CuCl.
- Formation conditions are provided by internal pressure in the CuCl nanodroplets.

An unexpected sequence of forming different crystal lattices for the CuCl nanophases in potassium aluminoborate glass depending on the preceding heat treatment temperature is revealed. The hexagonal wurtzite-like nanocrystals are shown to crystallize from the liquid CuCl nanosize droplets separated at the lower heat treatment temperatures (380 °C to no more than 400 °C) than in the case for the cubic sphalerite-like CuCl nanocrystals (higher than 400 °C). This sequence is inverse with respect to the standard temperature sequence of crystallizing the bulk hexagonal and cubic phases from a melt that is known for both CuCl and its structural prototype, ZnS. A tentative explanation for the effects revealed is proposed, the explanation assuming the principal role of internal pressure in the CuCl nanodroplets in setting the location of a phase point at the phase diagram.