Zn<sub>2</sub>MnSbO<sub>6</sub> and Zn<sub>2</sub>FeSbO<sub>6</sub>: Two New Polar\nHigh-Pressure Ordered Corundum-Type\nCompounds

Two new compounds, Zn<sub>2</sub>FeSbO<sub>6</sub> and\nZn<sub>2</sub>MnSbO<sub>6</sub>, have been synthesized under high-pressure\nand\nhigh-temperature conditions. The synthesis, single-crystal and powder\nX-ray diffraction, X-ray absorption near-edge spectroscopy (XANES),\noptical second harmonic generation (SHG), and magnetic and heat capacity\nmeasurements were carried out for both compounds and are described.\nThe lattice parameters are <i>a</i> = 5.17754(6) Å\nand <i>c</i> = 13.80045(16) Å for Zn<sub>2</sub>FeSbO<sub>6</sub> and <i>a</i> = 5.1889(10) Å and <i>c</i> = 14.0418(3) Å for Zn<sub>2</sub>MnSbO<sub>6</sub>. Single-crystal\nX-ray diffraction analyses indicate that Zn<sub>2</sub>FeSbO<sub>6</sub> consists of a cocrystal of superimposed Ni<sub>3</sub>TeO<sub>6</sub> (NTO) and ordered ilmenite (OIL) components with a ratio of approximately\n2:1 and Zn<sub>2</sub>MnSbO<sub>6</sub> contains two nearly identical,\nbut noncrystallographically related, OIL components in a ratio of\napproximately 6:1. XANES analysis shows Fe<sup>3+</sup> and Mn<sup>3+</sup> as formal oxidation states for Fe and Mn cations, respectively,\nfor these A<sub>2</sub>BB′O<sub>6</sub> compounds. SHG measurements\nfor Zn<sub>2</sub>MnSbO<sub>6</sub> indicate that it is noncentrosymmetric\nand confirm the polar <i>R</i>3 (no. 146) space group strongly\nimplied by single-crystal reflection data. The magnetic measurements\nreveal spin-glass behavior with antiferromagnetic (AFM) interactions\nin both compounds and a frustration factor (<i>f</i>) being\nsignificantly larger for Zn<sub>2</sub>MnSbO<sub>6</sub> (<i>f</i> ≈ 20) compared to Zn<sub>2</sub>FeSbO<sub>6</sub> (<i>f</i> ≈ 7). While Zn<sub>2</sub>FeSbO<sub>6</sub> exhibits AFM ordering at a Néel temperature (<i>T</i><sub>N</sub>) of 9 K, Zn<sub>2</sub>MnSbO<sub>6</sub> shows magnetic\nordering around 4 K. Additionally, the negative Curie–Weiss\ntemperatures for both compounds corroborate the presence of AFM exchange\ninteractions.