Synthesis, Characterization, and Structure-Property Relationships in Two New Polar Oxides: Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3)

Two new noncentrosymmetric (NCS) polar oxide materials, Zn-2(MoO4)(AO(3)) (A = Se4+ or Te4+), have been synthesized by hydrothermal and solid-state techniques. Their crystal structures have been determined, and characterization of their functional properties (second-harmonic generation, piezoelectricity, and polarization) has been performed. The isostructural materials exhibit a three-dimensional network consisting of Znat, ZnO6, MoO4, and AO(3) polyhedra that share edges and corners. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate the materials exhibit moderate SHG efficiencies of 100 x and 80 x alpha-SiO2 for Zn-2(MoO4)(SeO3) and Zn-2(MoO4)(TeO3), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d(33) values of similar to 14 and similar to 30 pm/V for Zn-2(MoO4)(SeO3) and Zn-2(MoO4)(TeO3), respectively, whereas pyroelectric measurements revealed coefficients of -0.31 and -0.64 mu C/m(2) K at SS degrees C for Zn-2(MoO4)(SeO3) and Zn-2(MoO4)(TeO3), respectively. Frequency-dependent polarization measurements confirmed that all of the materials are nonferroelectric; that is, the macroscopic polarization is not reversible, or "switchable". Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were also performed. First-principles density functional theory (DFT) electronic structure calculations were also done. Crystal data: Zn-2(MoO4)(SeO3), monoclinic, space group P2(1) (No. 4), a = 5.1809(4) angstrom, b = 8.3238(7) angstrom, c = 7.1541(6) angstrom, beta = 99.413(1)degrees, V = 305.2(1) angstrom(3), Z = 2; Zn-2(MoO4)(TeO3), monoclinic, space group P2(1) (No. 4), a = 5.178(4) angstrom, b = 8.409(6) angstrom, c = 7.241(5) angstrom, beta = 99.351(8)degrees, V = 311.1(4) angstrom(3), Z = 2.