  Crystals melt when thermal excitations or the concentration of defects in the
lattice is sufficiently high. Upon melting, the crystalline long-range order
vanishes, turning the solid to a fluid. In contrast to this classical scenario
of solid melting, here we demonstrate a counter-intuitive behavior of the
occurrence of crystalline long-range order in an initially disordered matrix.
This unusual solidification is demonstrated in a system of passive colloidal
particles accommodating chemically active defects -- photocatalytic Janus
particles. The observed crystallization occurs when the amount of
active-defect-induced fluctuations (which is the measure of the effective
temperature) reaches critical value. The driving mechanism behind this unusual
behavior is purely internal and resembles a blast-induced solidification. Here
the role of "internal micro-blasts" is played by the photochemical activity of
defects residing in the colloidal matrix. The defect-induced solidification
occurs under non-equilibrium conditions: the resulting solid exists as long as
a constant supply of energy in the form of ion flow is provided by the
catalytic photochemical reaction at the surface of active Janus particle
defects. Our findings could be useful for understanding of the phase
transitions of matter under extreme conditions far from thermodynamic
equilibrium.
