Synthesis, Structure, and Characterization of New Li⁺ – d⁰ –Lone-Pair – Oxides: Noncentrosymmetric Polar Li₆(Mo₂O₅)₃(SeO₃)₆ and Centrosymmetric Li₂(MO₃)(TeO₃) (M = Mo⁶⁺ or W⁶⁺)

Abstract

New quaternary lithium-d(0) cation-lone-pair oxides, Li(6)(Mo(2)O(5))(3)(SeO(3))(6) (Pmn2(1)) and Li(2)(MO(3))(TeO(3)) (P2(1)/n) (M = Mo(6+) or W(6+)), have been synthesized and characterized. The former is noncentrosymmetric and polar, whereas the latter is centrosymmetric. Their crystal structures exhibit zigzag anionic layers composed of distorted MO(6) and asymmetric AO(3) (A = Se(4+) or Te(4+)) polyhedra. The anionic layers stack along a 2-fold screw axis and are separated by Li(+) cations. Powder SHG measurements on Li(6)(Mo(2)O(5))(3)(SeO(3))(6) using 1064 nm radiation reveal a SHG efficiency of approximately 170 × α-SiO(2). Particle size vs SHG efficiency measurements indicate Li(6)(Mo(2)O(5))(3)(SeO(3))(6) is type 1 nonphase-matchable. Converse piezoelectric measurements result in a d(33) value of ∼28 pm/V and pyroelectric measurements reveal a pyroelectric coefficient of -0.43 μC/m(2)K at 50 °C for Li(6)(Mo(2)O(5))(3)(SeO(3))(6). Frequency-dependent polarization measurements confirm that Li(6)(Mo(2)O(5))(3)(SeO(3))(6) is nonferroelectric, i.e., the macroscopic polarization is not reversible, or 'switchable'. Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements and electron localization function calculations were also done for all materials.

Study of Integer Spin S = 1 in the Polar Magnet β-Ni(IO3)2

“…The lack of spatial inversion symmetry can stabilize asymmetric exchange interactions in systems with unpaired electrons, giving rise to novel physical phenomena such as multiferroics and topological spin textures [1][2][3][4][5][6]. However, engineering noncentrosymmetric (NCS) polar crystal structures for magnetic materials remains difficult, owing to a combination of several factors such as dipole-dipole interaction, steric effect, and thermodynamic effects, which often yield centrosymmetric lattices in transition metal complexes [7][8][9][10]. Polar asymmetric anions with stereo-active lone-pair electrons such as (SeO 3 ) 2− and (IO 3 ) − trigonal pyramids provide avenues for accessing NCS polar structures, facilitated by the second-order Jahn-Teller distortion [6,[11][12][13][14][15].…”

Synthesis and crystal structure of Fe6Ca2(SeO3)9Cl4 – a porous oxohalide

“…This kind of compound may show interesting physical properties such as magnetic frustration because of the increased possibility for metals to adopt low-dimensional arrangements in the crystal structure 6,7 or nonlinear optical second harmonic generation (SHG) because of the increased possibility to form noncentrosymmetric crystal structures due to the one-sided coordination of the lone-pair cations. [8][9][10] There are two main structure types for this family of oxohalide compounds: (i) layered compounds with strong covalent/ ionic bonds within the layers and weaker van der Waal interactions between the layers, e.g. Cu 3 (TeO 3 ) 2 Br 2 , Co 2 TeO 3 Cl 2 and FeTe 3 O 7 X (X = Cl, Br), 4,11,12 [13][14][15] The sizes of such channels are 3-4 Å in diameter at maximum and thus similar to the pore size in many zeolites; however they are not accessible for e.g.…”

Structural Diversity of Molybdate Iodate and Fluoromolybdate: Syntheses, Structures, and Calculations on Na3(MoO4)(IO3) and Na3Cs(MoO2F4)2

“…According to the concept proposed by Halasyamani and Poeppelmeier et al, these bond asymmetries: two “short”, two “long”, and two “intermediate” M–O/F bonds within the [MoO x F 6– x ] x − octahedron can be described as a C 2 (edge) distortion (Figure a). Similar 2 + 2 + 2 ( C 2 -axis distortion) bonding patterns are also observed in Na 2 Mo 2 O 5 (SeO 3 ) 2 , Li 6 (Mo 2 O 5 ) 3 (SeO 3 ) 6 , and CdTeMoO 6 . On the basis of the algorithm proposed by Halasyamani, the magnitudes of the out-of-center distortions of [Mo(1)­O 2 F 4 ] 2– and [Mo(2)­O 2 F 4 ] 2– are respectively calculated to be 0.845 and 0.832, which can be categorized as strong distortions .…”