  We show that a Tonks-Girardeau (TG) gas that is immersed in a Bose-Einstein
condensate can undergo a transition to a crystal-like Mott state with regular
spacing between the atoms without any externally imposed lattice potential. We
characterize this phase transition as a function of the interspecies
interaction and temperature of the TG gas, and show how it can be measured via
accessible observables in cold atom experiments. We also develop an effective
model that accurately describes the system in the pinned insulator state and
which allows us to derive the critical temperature of the transition.
