MnTaO₂N: Polar LiNbO₃‐type Oxynitride with a Helical Spin Order

Abstract

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO2N are reported. High-pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high-density structure containing middle-to-late transition metals. Synchrotron X-ray and neutron diffraction studies revealed that MnTaO2N adopts the LiNbO3-type structure, with a random distribution of O(2-) and N(3-) anions. MnTaO2N with an "orbital-inactive" Mn(2+) ion (d(5); S=5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] (δ≈0.3), which is different from the conventional G-type order observed in other orbital-inactive perovskite oxides and LiNbO3-type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO4N2 octahedral network combined with the mixed O(2-)/N(3-) species that results in a distribution of (super)-superexchange interactions.

KCl flux-induced growth of isometric crystals of cadmium-containing early transition-metal (Ti 4+ , Nb 5+ , and Ta 5+ ) oxides and nitridability to form their (oxy)nitride derivatives under an NH 3 atmosphere for water splitting application

“…The authors of the present work believe that these crystal phases may still be possible to form by other synthesis techniques, including high-pressure approach [48]. Under high-temperature NH 3 atmosphere, only Cd 2 Ta 2 O 7 was fully converted to single-phase Ta …”

Metal oxynitrides as emerging materials with photocatalytic and electronic properties

“…Classical ferroelectricity has been recently observed in compressively strained SrTaO 2 N epitaxial thin films grown on SrTiO 3 substrates. 5) 23 It is insulating, and dielectric measurements have not been reported, but the calculated spontaneous polarization is similar to multiferroic Mn oxides with a LiNbO 3 structure. 103 Recently the new structurally related oxynitride MnTaO 2 N with a polar LiNbO 3 -type structure has been reported.…”

“…23 These are still scarce because the higher electronegativity of metals like Fe, Mn or Co promotes the formation of interstitial binary nitrides under the reducing conditions of N 2 or under NH 3 at high temperatures. The consequences of introducing nitride into an oxidic network are relevant on physical and chemical properties because of differences in charge, electronegativity and polarizability of both anions.…”

High‐Pressure Synthesis of Manganese Oxyhydride with Partial Anion Order

“…Inequivalent Mn-O-Mn and Mn-H-Mn bonds for each J 1i (i = a, b, c) may also account for the enhanced frustration. In fact, Mn 2+ TaO 2 Nh as al arger f of 9.2 [20] than the isostructural oxide Mn 2+ TiO 3 with f = 6, [21] resulting in different spin structures.…”

“…[9] Unlike ABO 3 ,t he pristine A 2 BO 4 affords two distinct crystallographic oxygen sites:t he axial O2 site surrounded by five A and one Ba toms and the equatorial O1 site surrounded by four Aand two Batoms.Since the Acation in A 2 BO 3 Xisin general more electropositive,there is atendency that amore/ less electronegative anion occupies the O1/O2 site. [20,21] Such anion order is often encountered in oxyfluorides with F À at the axial site (Sr 2 CoO 3 F, Sr 2 NiO 3 F), [24,25] in oxynitrides with N 3À at the equatorial site (Sr 2 TaO 3 N, Sr 2 NbO 3 N), [23,26] though few exceptions like Nd 2 AlO 3 Ne xist. [27] Given the electronegativity of H(2.2), H À is likely to occupy the O1 site,which is what has been observed previously in Sr 2 VO 3 H, [9] LaSr-CoO 3 H 0.7 , [4] and now in LaSrMnO 3.3 H 0.7 .…”