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, Zn2(MoO4)(AO3) (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 ZnO4, ZnO6, MoO4, and AO3 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 × and 80 × α-SiO2 for Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d33 values of ∼14 and ∼30 pm/V for Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3), respectively, whereas pyroelectric measurements revealed coefficients of −0.31 and −0.64 μC/m2 K at 55 °C for Zn2(MoO4)(SeO3) and Zn2(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: Zn2(MoO4)(SeO3), monoclinic, space group P21 (No. 4), a = 5.1809(4) Å, b = 8.3238(7) Å, c = 7.1541(6) Å, β = 99.413(1)°, V = 305.2(1) Å3, Z = 2; Zn2(MoO4)(TeO3), monoclinic, space group P21 (No. 4), a = 5.178(4) Å, b = 8.409(6) Å, c = 7.241(5) Å, β = 99.351(8)°, V = 311.1(4) Å3, Z = 2.