Zn₂MnSbO₆ and Zn₂FeSbO₆: Two New Polar High-Pressure Ordered Corundum-Type Compounds

Two new compounds, Zn2FeSbO6 and Zn2MnSbO6, have been synthesized under high-pressure and high-temperature conditions. The synthesis, single-crystal and powder X-ray diffraction, X-ray absorption near-edge spectroscopy (XANES), optical second harmonic generation (SHG), and magnetic and heat capacity measurements were carried out for both compounds and are described. The lattice parameters are a = 5.17754(6) Å and c = 13.80045(16) Å for Zn2FeSbO6 and a = 5.1889(10) Å and c = 14.0418(3) Å for Zn2MnSbO6. Single-crystal X-ray diffraction analyses indicate that Zn2FeSbO6 consists of a cocrystal of superimposed Ni3TeO6 (NTO) and ordered ilmenite (OIL) components with a ratio of approximately 2:1 and Zn2MnSbO6 contains two nearly identical, but noncrystallographically related, OIL components in a ratio of approximately 6:1. XANES analysis shows Fe3+ and Mn3+ as formal oxidation states for Fe and Mn cations, respectively, for these A2BB′O6 compounds. SHG measurements for Zn2MnSbO6 indicate that it is noncentrosymmetric and confirm the polar R3 (no. 146) space group strongly implied by single-crystal reflection data. The magnetic measurements reveal spin-glass behavior with antiferromagnetic (AFM) interactions in both compounds and a frustration factor (f) being significantly larger for Zn2MnSbO6 (f ≈ 20) compared to Zn2FeSbO6 (f ≈ 7). While Zn2FeSbO6 exhibits AFM ordering at a Néel temperature (TN) of 9 K, Zn2MnSbO6 shows magnetic ordering around 4 K. Additionally, the negative Curie–Weiss temperatures for both compounds corroborate the presence of AFM exchange interactions.