BaSiP: 1D Nonlinear Optical Material with Thermal Barrier Chains.

A novel barium silicon phosphide was synthesized and characterized. BaSiP crystallizes in the noncentrosymmetric space group 2 (No. 33) and exhibits a unique bonding connectivity in the Si-P polyanion not found in other compounds. The crystal structure is composed of SiP tetrahedra connected into one-dimensional double-tetrahedra chains through corner sharing, edge sharing, and covalent P-P bonds. Chains are surrounded by Ba cations to achieve an electron balance. The novel compound exhibits semiconducting properties with a calculated bandgap of 1.6 eV and experimental optical bandgap of 1.88 eV. The complex pseudo-one-dimensional structure manifests itself in the transport and optical properties of BaSiP, demonstrating ultralow thermal conductivity (0.56 W m K at 300 K), promising second harmonic generation signal (0.9 × AgGaS), as well as high laser damage threshold (1.6 × AgGaS, 48.5 MW/cm) when compared to the benchmark material AgGaS. Differential scanning calorimetry reveals that BaSiP melts congruently at 1373 K, suggesting that large single crystal growth may be possible.