 To whom correspondence should be addressed. Fax: #81-46-240- 4722. E-mail: sekar@with.brl.ntt.co.jp. Journal of Solid State Chemistry 156, 422 } 427 (2001) doi:10.1006/jssc.2000.9017, available online at http://www.idealibrary.com on Crystal Growth, Structure, and Transport Properties of the Five-Leg Spin Ladder Compound La 8 Cu 7 O 19 C. Sekar, T. Watanabe, A. Matsuda, and H. Shibata NTT Basic Research Laboratories, 3-1 Wakamiya Morinosato, Atsugi-shi, Kanagawa 243-0198, Japan and Y. Zenitani and J. Akimitsu Department of Physics, Aoyama Gakuin University, 6-16-1 Chitosedai, Setagaya-ku, Tokyo 157-8572, Japan Received July 5, 2000; in revised form October 13, 2000; accepted October 27, 2000 The crystallization region of La 8 Cu 7 O 19 exists in a narrow temperature (1045+10503C) and composition range (1:4.5+ 1:5.0; La 2 O 3 :CuO molar ratio) in the La 2 O 3 +CuO system in an air ambient. In this narrow range, we have succeeded in growing large La 8 Cu 7 O 19 single crystals, for the 5rst time, by a modi5ed slow cooling method. Single-crystal X-ray di4raction analysis reveals that La 8 Cu 7 O 19 crystallizes in a monoclinic structure with space group C2/c and has the lattice parameters a  13.82(7) A  , b  3.734(8) A  , c  34.77(10) A  , and   99.3(4)3. The electrical transport behavior of the as-grown and hole-doped La 8 Cu 7 O 19 single crystals are semiconducting. A lowest resistivity of 11.0 m-cm is measured at 293 K along the ladder direction ( b-axis) for the hole-doped samples.  2001 Academic Press Key Words: spin ladder; La 8 Cu 7 O 19 single crystals; structure; transport property. 1. INTRODUCTION The study of spin ladders, composed of S"  antifer- romagnetically coupled chains, has been emerging as one of the active areas of research in the "eld of high-Tc supercon- ductivity. It is now well known that the ladders with even and odd number of legs have quite generic features, such as the presence of a spin gap at half-"lling in even-leg systems and its absence in odd-leg ladders (1). The possibility of superconductivity has been predicted for an even-leg ladder system lightly doped with holes (1) and, subsequently, the two-leg ladder compound (Sr  Ca  )  Cu  O  was dis- covered to be superconducting at 12 K under high pressure of 3 GPa (2). In the case of odd-leg ladders, it has been predicted that they might exhibit properties similar to single chains at low energies (1). It has been experimentally proved that the magnetic properties of the well-known odd-leg ladder compound Sr  Cu  O  (three-leg) are consistent with the theoretical predictions (3). However, this compound could be synthesized only under high pressure and also hole-doping is di$cult. Hence, transport properties have not been studied. The compound La  Cu  O  , n"3 member of the new homologous series of lanthanum cuprates La  Cu  O  , consists of "ve-legs, and it is also asserted to lack a spin gap in its magnetic excitation spectrum (4, 5). Re- cently, Zenitani et al. (6) succeeded in hole-doping polycrys- talline La  Cu  O  by means of high-oxygen-pressure annealing using a hot-isostatic-pressing (HIP) furnace. A signi"cant decrease in the resistivity was observed in those samples, although no transition was observed from the semiconducting behavior. Single crystals are more suit- able for studying both the doping e!ect and the anisotropic properties. However, there have been no reports on crystal growth because La  Cu  O  was thought to have no tem- perature interval where La  Cu  O  could exist in equilib- rium with the liquidus (4, 7). During the course of our recent attempts to crystallize La  Cu  O  (four-leg), n"2 member of the same homologous series, we found that in ambient air the La  Cu  O  cocrystallizes with La  Cu  O  (as mixed crystals) in a small temperature interval between 1045 and 10503C (8). This very narrow equilibrium range makes it di$cult to crystallize La  Cu  O  by a standard slow cool- ing (SSC) method. In this paper, the preparation of La  Cu  O  single crystals by a modi"ed slow cooling method and characterization of those crystals with respect to their structure, elemental composition, and transport properties are presented. 422 0022-4596/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.