Preparation and characterization of powders and crystals of V n‐x Ti x O 2n‐1 Magneli oxides

• Published in: Crystal research and technology (1979) Vol. 40; no. 10-11; pp. 1067 - 1071
• Main Authors: Calestani, D., Licci, F., Kopnin, E., Calestani, G., Gauzzi, A., Bolzoni, F., Besagni, T., Boffa, V., Marezio, M.
• Format: Journal Article
• Language: English
• Published: 01-11-2005
• ISSN: 0232-1300; 1521-4079
• DOI: 10.1002/crat.200410488

Abstract
V
n‐x
Ti
x
O
2n‐1
Magnéli phases have been synthesized under vacuum in powder form (n = 4, 0 ≤ x ≤ 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl
4
and NH
4
Cl were used as transporting agents. Needle‐shaped crystals as long as 200‐300 micrometers or 2‐3 mm were obtained when in presence of NH
4
Cl or TeCl
4
, respectively. The powder and crystal structures were examined by X‐ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single‐phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X‐ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Végard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P‐1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four‐points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V
4
O
7
. The metal‐insulator transitions observed in V
4
O
7
and V
5
O
9
, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)