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

Abstract

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 (T_N) 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.