Synthesis and phase width of quaternary selenides Pb₄ln _xM_6-XSe₁₃ (M = Bi, X= 2.1-2.8; Sb, X= 2)

Quaternary selenldes of Pb₄In_xM_6-xSe ₁₃ (M = Bi, x= 2.1 -2.8; Sb, x=2) were synthesized by solid-state methods, and their structures were determined from X-ray diffraction of single crystals. These compounds are isostructural with Pb₄In ₂Bi₄S₁₃ and crystallize In orthorhombic space group Pbam (No. 55) with Z= 4; the structure features a threedimensional framework consisting of Z-shaped ribbon units and corner-sharing infinite one-dimensional [InSe₄]_∞ chains running parallel to the o-axis, which are connected by Pb atoms to form a three-dimensional structure. Calculations of the band structure and measurements of Seebeck coefficient, electrical conductivity, and diffuse reflectance spectra confirm that these compounds are semiconductors with a narrow band gap. All compounds show semiconducting properties; the Seebeck coefficient of Pb₄In _2.5Bi_3.5Se₁₃ Is -180 μV/K at 295 K.