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The ternary half-Heusler compounds have shown great potential for realizing new 3D topological insulators. With band gap tuning and spin orbit coupling these compounds may undergo topological phase transitions. In present work, we explore the possibility of realizing a topological insulating phase in half-Heusler family NaYO (Y = Ag, Au, and Cu). We find that for NaAgO, external strain ($\sim$19 \%) along with spin-orbit coupling, is required to achieve band-inversion at $\Gamma$ high-symmetry point and leads to phase transition from trivial to non-trivial topological insulating phase. In case of NaAuO and NaCuO, non-trivial phase appears in their equilibrium lattice constant, hence only spin-orbit coupling is enough to achieve band-inversion leading to non-trivial topology. The non-centrosymmetric nature of crystal geometry leads to the formation of two twofold degenerate point nodes near the Fermi level.

The effects of compressive strain, doping and temperature on the thermoelectric properties of CH3NH3PbI3 have been investigated by employing first principles based calculations and semi-classical Boltzmann theory. CH3NH3PbI3 displays a topological phase transition under 9.9% external compressive strain. Thermoelectric studies reveal that application of strain enhances the Seebeck coefficient for electron and hole-doped regions. This increment is attributed to the strain induced band inversion and modifications in the electronic density of states at the topological transition point. The strain driven topological phase transition produces a ZT value of 0.89 for hole-doped CH3NH3PbI3 at 800 K.

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