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/infinity[Nb2PSe10 ] chains separated by alkali cations. The chains consist of [Nb-2(Se-2)(2)](4+) clusters bridged by a diselenide and a [PSe4](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 NbSe3 and Nb2Se9 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 degrees 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 Omega center dot cm. Nonlinear optical second harmonic generation measurements were done on the Rb analog yielding a chi(2) of similar to 7 pm/V and showing phase matching behavior.