Semiconducting Properties and Phase-Matching Nonlinear Optical Response of the One-Dimensional Selenophosphates ANb₂PSe₁₀ (A = K, Rb, and Cs)

The new compounds ANb 2 PSe 10, where A = K, Rb and Cs, form from polyselenophosphate flux reactions and crystallize in the noncentrosymmetric space group Pc . They feature infinite one-dimensional 1 / ∞ [Nb 2 PSe 10 – ] chains separated by alkali cations. The chains consist of [Nb 2 (Se 2 ) 2 ] 4+ clusters bridged by a diselenide and a [PSe 4 ] 3– group. The chains pack differently depending on which alkali cation is present in the lattice. As a result, the analogs are not isostructural with respect to each other, and each has a different unit cell. The reaction chemistry involving a multitude of reaction conditions and their respective products is discussed. Other products from these reactions include NbSe 3 and Nb 2 Se 9 in both crystalline and microfibrous morphologies. The ANb 2 PSe 10 compounds are stable to oxidation in ambient air but decompose when heated above 350 °C. Their band gaps were measured to be 1.1–1.2 eV and the resistivity of the K analog at room temperature was measured at 4.5 Ω·cm. Nonlinear optical second harmonic generation measurements were done on the Rb analog yielding a χ 2 of ∼7 pm/V and showing phase matching behavior.