  For topological insulators and topological crystalline insulators (TCIs),
their exotic surface states are promising for fundamental condensed matter
physics research as well as future electronics such as low-dissipation
electronics and spintronics. However, the high bulk carrier density that often
dominates the transport property is the major materials challenge, critically
hindering our ability to study and manipulate the surface states. In this
manuscript, we demonstrate an alloying strategy, SnSexTe1-x, to effectively
reduce the bulk carrier density. As long as SnSexTe1-x remains in the cubic
crystal structure, it is predicted to be a TCI. We show systematic decrease of
the bulk carrier density with the increasing Se concentration, demonstrating
that the alloying principle works. In addition, we map out the phase diagram of
the cubic to the orthorhombic structural transition as a function of the Se
concentration. This was made possible by studying alloy nanoplates which remain
single-crystalline and is either in the cubic or the orthorhombic phase, in
contrast to bulk alloys that would exhibit polycrystalline grains. Lastly, we
investigate systematically the ferroelectric transition associated with the
structural transition from the cubic to the rhombohedral phase for SnSexTe1-x.
This is the first ferroelectric transition study of the alloy system
SnSexTe1-x.
