Ba2Si3P6: 1D Nonlinear Optical Material with Thermal Barrier Chains

A novel barium silicon phosphide was synthesized and characterized. Ba 2 Si 3 P 6 crystallizes in the noncentrosymmetric space group Pna 2 1 (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 4 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 Ba 2 Si 3 P 6, demonstrating ultralow thermal conductivity (0.56 W m –1 K –1 at 300 K), promising second harmonic generation signal (0.9 × AgGaS 2 ), as well as high laser damage threshold (1.6 × AgGaS 2, 48.5 MW/cm 2 ) when compared to the benchmark material AgGaS 2 . Differential scanning calorimetry reveals that Ba 2 Si 3 P 6 melts congruently at 1373 K, suggesting that large single crystal growth may be possible.