Über Oxotantalate der Lanthanide des Formeltyps MTaO₄ (M = La – Nd, Sm – Lu)

Abstract

About Lanthanide Oxotantalates with the Formula MTaO4 (M = La – Nd, Sm – Lu)Besides being a by‐product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO4 can be easily prepared by sintering lanthanide sesquioxide M2O3 and tantalum(V) oxide Ta2O5 with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M3+ cationic radius. For M = La – Pr the MTaO4‐type tantalates crystallize in the space group P21/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A‐type) and as trigonal dodecahedron for the structure with the smaller ones (called as B‐type in the following). The coordination environment about the Ta5+ cations can be described as a slightly distorted octahedron (CN = 6) for the A‐type structure of MTaO4 and a heavily distorted one (CN = 6) for the B‐type. The difference between the two types results from the interconnection of these [TaO6]7− octahedra. Whereas they are connected via four vertices to form corrugated layers according to $^{2}_{\infty}\rm[TaO^{v}_{4/2}O^{t}_{2/2}]^{3-}$ parallel the bc‐plane in the A‐type, the octahedra of the B‐type MTaO4 structure share edges to built up zig‐zag chains $^{1}_{\infty}\rm[TaO^{e}_{4/2}O^{t}_{2/2}]^{3-}$ along the c axis.

Charge transfer transitions in the transition metal oxides ABO4:Ln3+ and APO4:ln3+ (A=La, Gd, Y, Lu, Sc; B=V, Nb, Ta; Ln=lanthanide)

“…Eq. (1) can be applied also to express the band gap energy of binary compounds with formula M m X n or compounds containing complexes of the from MX qÀ n [44].…”

Effect of the processing parameters on the crystalline structure of lanthanide orthotantalates

“…The focus of this work is the lanthanide orthotantalates (LnTaO 4 ), which belong to the class of electroceramics and have been extensively studied in recent years because of their huge range of environmental-and energy-related applications 8,9 . A series of polymorphic modifications, which belong to the structures usually found in BaMnF 4 , M-and M'-fergusonite and scheelite, are known for LnTaO 4 compounds [10][11][12][13] . The samples with larger ionic radius of Ln (Ln = La-Pr) exhibit two perovskite-like layered polymorphic modifications with monoclinic LaTaO 4 -type and BaMnF 4 -type structures.…”

“…The other lanthanides (Ln = Nd-Lu) crystallize in the monoclinic form, besides their ability to possess two fergusonite-type structures. The first one belongs to the space group I2/a, known as M-type structure, while the second one belongs to the space group P2/a, called M'-type structure 10,13,14 . Implementation of either of these structure types for LnTaO 4 depends not only on the Ln atomic radius, but also on the synthesis conditions during the different sample preparation procedures.…”

“…Implementation of either of these structure types for LnTaO 4 depends not only on the Ln atomic radius, but also on the synthesis conditions during the different sample preparation procedures. This leads to numerous disagreements in the data about how the structural stability ranges as well as in the regions where the polymorphic modifications occur, including their crystal structure and other properties for LnTaO 4 [11][12][13][14][15] . Lanthanide orthotantalates can be prepared by different techniques.…”

Two Ta2O5‐Rich Alkali‐Metal Lanthanide(III) Oxotantalates(V): K2LaTa5O15 and NaTm2Ta15O41

“…In the field of lanthanide‐containing oxotantalates(V) EuTa 2 O 6 and Eu 2 Ta 2 O 7 were two compounds, which first occurred as side products 1. Other examples for those by‐products from tantalum containers are the A ‐ and B ‐type series of the ternary oxotantalates(V) M TaO 4 ( M = La–Lu) 2, the new C ‐type structure of LaTaO 4 3, SmTa 7 O 19 4 or NdFTa 2 O 6 and La 3 Cl 3 TaO 5 F 5. But also binary halides such as TaI 4 6, selenides such as Ta 2 Se 7 or tellurides with various compositions (e.g.…”