TY - JOUR

T1 - Perovskite tungsten bronze-type crystals of LixWO3 grown by chemical vapour transport and their characterisation

AU - Rüscher, Claus H.

AU - Dey, Kalpana R.

AU - Debnath, Tapas

AU - Horn, Ingo

AU - Glaum, Robert

AU - Hussain, Altaf

N1 - Funding Information: This work has been supported in part by the “Alexander von Humboldt Stiftung” under collaborative research program (V-FOKOOP/DEU/1062067/Hussain) and DFG (RU764/4-1). K.R. Dey is grateful for the “Lichtenberg Stipendium” of the “Land Niedersachsen” (Germany) for the support of her Ph.D. work and to Prof. Binnewies (ACI, Leibniz University Hannover) for the support with crystal growth facilities. Finally, the authors are thankful to three unknown referees and to the editor for helpful comments.

PY - 2008/1

Y1 - 2008/1

N2 - Crystals of LixWO3 with nominal compositions, x=0.1, 0.25, 0.3, 0.35, 0.4 and 0.45 were grown by chemical vapour transport method using HgCl2 as transporting agent. A complete transport was achieved with a temperature gradient T1/T2=800/700 °C revealing bluish-black crystals of sizes up to a few 10th of a millimeter. X-ray powder diffraction and infrared (IR) absorption spectra show Perovskite tungsten bronze of cubic symmetry (PTBc) for x=0.45 and 0.4, mixed phase of PTBc and Perovskite tungsten bronze of tetragonal symmetry (PTBt) for x=0.35, 0.3 and 0.25 and of PTBt and Perovskite tungsten bronze of orthorhombic symmetry (PTBo) for x=0.1. The structure of PTBt is explained by the off centring of the W-ions along c and tilting of the WO6 octahedra around c. Crystal slices of mixed phase (i.e. PTBc and PTBt) reveal bright and dark areas on a sub-millimeter scale which are separated by sharp interfaces. Laser ablation inductively coupled plasma optical emission (LA ICP OES) analysis on small spot sizes show the separation into Li contents of x=0.18 (bright areas) and x=0.38 (dark areas) as threshold compositions of PTBt and PTBc, respectively. Polarized reflectivity using a microscope technique in the bright area of the crystals indicates strong anisotropic absorption effects with maximum between 1000 and 6000 cm-1, which are related to optical excitations of polarons. Crystals of composition x=0.4 and 0.45 appear optically homogeneous and show an effective "free carrier-type plasma frequency" (wp) of about 12,900 and 13,700 cm-1, respectively.

AB - Crystals of LixWO3 with nominal compositions, x=0.1, 0.25, 0.3, 0.35, 0.4 and 0.45 were grown by chemical vapour transport method using HgCl2 as transporting agent. A complete transport was achieved with a temperature gradient T1/T2=800/700 °C revealing bluish-black crystals of sizes up to a few 10th of a millimeter. X-ray powder diffraction and infrared (IR) absorption spectra show Perovskite tungsten bronze of cubic symmetry (PTBc) for x=0.45 and 0.4, mixed phase of PTBc and Perovskite tungsten bronze of tetragonal symmetry (PTBt) for x=0.35, 0.3 and 0.25 and of PTBt and Perovskite tungsten bronze of orthorhombic symmetry (PTBo) for x=0.1. The structure of PTBt is explained by the off centring of the W-ions along c and tilting of the WO6 octahedra around c. Crystal slices of mixed phase (i.e. PTBc and PTBt) reveal bright and dark areas on a sub-millimeter scale which are separated by sharp interfaces. Laser ablation inductively coupled plasma optical emission (LA ICP OES) analysis on small spot sizes show the separation into Li contents of x=0.18 (bright areas) and x=0.38 (dark areas) as threshold compositions of PTBt and PTBc, respectively. Polarized reflectivity using a microscope technique in the bright area of the crystals indicates strong anisotropic absorption effects with maximum between 1000 and 6000 cm-1, which are related to optical excitations of polarons. Crystals of composition x=0.4 and 0.45 appear optically homogeneous and show an effective "free carrier-type plasma frequency" (wp) of about 12,900 and 13,700 cm-1, respectively.

KW - Crystal growth

KW - Optical properties

KW - Perovskite tungsten bronzes

KW - Polarons

UR - http://www.scopus.com/inward/record.url?scp=37549044717&partnerID=8YFLogxK

U2 - 10.1016/j.jssc.2007.10.033

DO - 10.1016/j.jssc.2007.10.033

M3 - Article

AN - SCOPUS:37549044717

VL - 181

SP - 90

EP - 100

JO - Journal of solid state chemistry

JF - Journal of solid state chemistry

SN - 0022-4596

IS - 1

ER -