K₂CaV₂O₇: a pyrovanadate with a new layered type of structure in the A₂BV₂O₇family

Abstract

The crystal structure of K(2)CaV(2)O(7) prepared by a conventional solid-state reaction has been solved by a direct method and refined using Rietveld full profile fitting based on X-ray powder diffraction data. This compound crystallises in the triclinic space group (P1, Z = 2) with unit cell constants a = 7.1577(1) Å, b = 10.5104(2) Å, c = 5.8187(1) Å, α = 106.3368(9)°, β = 106.235(1)°, γ = 71.1375(9)°. The structure can be described as infinite undulating CaV(2)O(7)(2-) layers parallel to the ac plane, which consist of pairs of edge-sharing CaO(6) octahedra connected to each other through V(2)O(7) pyrogroups. The potassium atoms are positioned in two sites between the layers, with a distorted IX-fold coordination of oxygen atoms. The chemical composition obtained from the structural solution was confirmed by energy-dispersive X-ray analysis. The stability of compounds in the family of alkali metal calcium pyrovanadates is discussed based on an analysis of the correlation between anion and cation sizes and theoretical first-principles calculations.

Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides

“…The transformation of SrCrO 3 to 15R-SrCrO 2.8 can be understood by the crystal field stabilization of Cr 4+ (d 2 ) in tetrahedral coordination 33 . Since the tetrahedral vanadium in our case is exclusively pentavalent [34][35][36] , the tetrahedral coordination preference should also be the origin of this phase stabilization where SrV 4+ O 3 (or SrV 4+ O 3-2x/3 N x ) is oxidized by aliovalent N 3-/O 2exchange. Although diffusion of nitride anions requires larger activation energy relative to oxide anion 37 , perovskite-based compounds with AO 2 layers have shown rapid oxide ion conduction [38][39][40] .…”

Electrical properties and complex impedance analysis of K2ZnV2O7

“…In the literature, many layered double vanadates of A I 2 B II V 2 O 7 (A = alkali metal, B = bivalent metal) formulation have been studied with A = Na, K, Rb, Cs and B = Zn, Ca, Mg, Mn [6]. Bidimensional structures of these vanadates are characterized by the association of BO m polyhedral and V 2 O 7 pyrovanadates groups.…”

Crystal structure of RbBaVO4 and high-pressure modification of KCaVO4

“…To our knowledge, there are only four references concerning the crystal structure of compounds in the K 2 O-CaO-V 2 O 5 and Rb 2 O-BaO-V 2 O 5 systems that describe KCa 10 V 7 O 28 (Schrandt and Müller-Buschbaum, 1996), K 3 CaV 5 O 15 (Martin and Müller-Buschbaum, 1995), K 2 CaV 2 O 7 (Tyutyunnik et al, 2013) and Rb 4 Ba(VO 3 ) 6 (Zubkov et al, 2008). At the same time, the PDF2 database has 10 entries for these two systems.…”