electric” phase transition. Therefore, the sample with x = 0.35 (i.e., z = 0.5) located at the boundary exhibits a very high hys- teresis-free electrostrictive strain (∼ 0.1 %) with a electrostric- tive coefficient Q of ∼ 10 –2 m 4 C –2 . This indicates that the system is very promising for practical applications as a lead- free electrostrictive material. Experimental The samples of SrTiO 3 doped with Bi and Na were prepared by the solid-state reaction method. The composition was (Sr 1–y–x–f Na y- Bi x & f )TiO 3 (denoted as SNBT, where & represents Sr vacancies) with y = 0.5z, x = 0.2 + 0.3z, f = 0.1–0.1z, and z = 0, 0.05, 0.1, 0.3, 0.5, and 0.65. The dielectric properties were measured in the temperature range of 12–500 K. The polarization and strain were measured at room temperature by a Sawyer–Tower circuit and a linear variable- displacement transducer driven by a lock-in amplifier, respectively. X-ray diffraction analysis showed that all compositions were of sin- gle-phase perovskite structures at room temperature. Received: May 9, 2005 Final version: August 25, 2005 Published online: November 15, 2005 – [1] M. E. Lines, A. M. Glass, Principles and Applications of Ferroelec- trics and Related Materials, Clarendon, Oxford, UK 1977. [2] J. C. Burfoot,G. W. Taylor, Polar Dielectrics and Their Applications, Macmillan, London 1979. [3] K. Uchino, S. Nomura, L. E. Cross, S. J. Jang, R. E. Newnham, J. Appl. Phys. 1980, 51, 1142. [4] S.-E. Park, T. R. Shrout, P. Bridenbaugh,J. Rotterberg, G. M. Loia- cono, Ferroelectrics 1998, 207, 519. [5] C. Ang, Z. Yu, J. Appl. Phys. 2002, 91, 1487. [6] C. Ang, J. F. Scott, Z. Yu, H. Ledbetter, J. L. Baptista, Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 6661. [7] C. Ang, Z. Yu, J. Hemberger, P. Lunkhemer, A. Loidl, Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 6665. [8] C. Ang, Z. Yu, P. Lunkhemer,J. Hemberger, A. Loidl, Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 6670. [9] C. Ang, Z. Yu, Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61, 11 363. [10] T. Takenaka, Ferroelectrics 1999, 230, 389. [11] C.-S. Tu, I. G. Siny, V. H. Schmidt, Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 11 550. [12] I. G. Siny, C.-S. Tu, V. H. Schmidt, Phys. Rev. B: Condens. Matter Mater. Phys. 1995, 51, 5659. [13] For (Sr 1–1.5x Bi x  0.5x )TiO 3 , from T m = 123 K at x = 0.04 to T m = 198 K at x = 0.2, we obtain a shifting rate of ∼ 4.71 K/1 mol-% Bi ions. For Bi and Na co-doped (Sr 1–y–x–f Na y Bi x )TiO 3 , as x = 0.395 (at z = 0.65), T m = 318 K; but according to the rate of 4.71 K/1 mol-% Bi ions, the T m should be 290 K. The extra increase 28 K can be reasonably at- tributed to the contribution of Na doping. In this case, since the con- centration of Na is y = 0.325 at z = 0.65, we see a shifting rate for T m of Na of ∼ 0.86 K/1 mol-% Na ions. [14] R. D. Shannon, Acta Crystallogr., Sect. A: Cryst.Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 752. DOI: 10.1002/adma.200501735 WS 2 Closed Nanoboxes Synthesized by Spray Pyrolysis By Stéphane Bastide,* Dominique Duphil, Jean-Pascal Borra, and Claude Lévy-Clément Inorganic, layered compounds are known to adopt nested, spherical structures at the nanoscale in the form of fullerene- like particles [1] and nanotubes. [2,3] The first discovered and best-known examples are transition-metal dichalcogenides MX 2 (M = Mo, W, and X = S, Se). Here, we report on a new type of WS 2 nested nanoparticles that exhibit a cuboid form of a rectangular parallelepiped, rather than the usual spherical morphology. [4] These cuboids possess a hollow core sur- rounded by walls made up of stacked layers, hence presenting the structure of a closed nanobox. They are obtained by spray pyrolysis of ammonium tetrathiotungstate solutions at high temperature, a new promising route for the synthesis of WS 2 nested materials. In an ongoing research effort devoted to finding new routes for the synthesis of fullerene-like WS 2 particles, we have tried to combine the well-known decomposition of ammonium tet- rathiotungstate into WS 2 at high temperature with the ability of the spray-pyrolysis technique to form solid particles out of droplets of suitable liquid-containing precursors. For this purpose, we sprayed various ammonium tetrathiotungstate ((NH 4 ) 2 WS 4 ) solutions with a pneumatic-spray apparatus using an inert carrier gas and generating micrometer-sized droplets directly connected to the quartz tube of a tubular fur- nace. According to the literature, the reaction mechanism for the decomposition of (NH 4 ) 2 WS 4 by pyrolysis is as follows: [5,6] (NH 4 ) 2 WS 4 → WS 3 +H 2 S + 2NH 3 ∼ 170 °C (1) WS 3 → a-WS 2 +S ∼ 280 °C (2) a-WS 2 → c-WS 2 ∼ 450 °C (3) where a-WS 2 designates amorphous WS 2 . Eventually, the so- lid particles thus synthesized and transported by the gas flow are collected on a filter as a powder (see Experimental). COMMUNICATIONS 106 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2006, 18, 106–109 ______________________ – [*] Dr. S. Bastide, Dr. D. Duphil,Dr. C. Lévy-Clément Laboratoire de Chimie Métallurgique des Terres Rares (LCMTR) Centre National de la Recherche Scientifique (CNRS), UPR 209 2/8 rue Henri Dunant, F-94320 Thiais Cedex (France) E-mail: bastide@glvt-cnrs.fr Dr. J.-P. Borra Laboratoire de Physique des Gaz et des Plasmas (LPGP), UMR 8578 Centre National de la Recherche Scientifique (CNRS) École Supérieure d’Électricité (SUPELEC) Plateau de Moulon, 3 rue Joliot-Curie, F-91192 Gif/Yvette (France)