We have investigated the electronic and thermoelectric properties of \(\hbox {Ca}_3\hbox {P}_2\) in both cubic and hexagonal forms using first-principles calculations and Boltzmann transport theory from 100 K to 1200 K. The calculated band structure reveals a low bandgap (0.32 eV) semiconducting behavior for the cubic phase, whereas the hexagonal phase exhibits a semimetallic nature with no bandgap. Both structures show a large negative Seebeck coefficient at low temperatures, which is slightly lower for the hexagonal structure and decreases with increasing temperature. The electrical conductivity increases with temperature and is higher in the hexagonal phase due to its semimetallic nature. The thermal conductivity also increases with temperature and is greater in hexagonal form. The thermoelectric figure of merit (ZT) reaches a maximum of approximately 1 for both phases at 100 K. Moreover, for the hexagonal structure, it remains around 1 over the temperature range of 100–400 K, suggesting that the material exhibits promising thermoelectric performance around room temperature.
