Supplement to Z. Phys. D 26, S 234-236 (1993) Atoms, Molecules and Clusters vat Ohy~ D © Springer-Veflag 1993 Suppression of superconductivity in submicron LaLssSroasCuO4_6 V. R. Palkar 1, P. Ayyub 1, D. R. Nepali 2 and M. S. Multani 1 l Materials Research Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India 2Hot Laboratory, Tam Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India Abstract. Bulk Lal.85Sr0.1sCuO4.~ (LSCO) superconducts below 36K. But microcrystalline LSCO with mean panicle size <700nm (prepared by rapid liquid dehydration) is not superconducting down to 4.2K. This may be due to a size- induced structural distortion and an accompanying reduction in the oxygen occupancy. PACS: 74.70.Mq;81.35.+k 1. Introduction Size effects play an important role in superconducti- vitv. These are manifested when the physical dimen- sion of a sample (e.g., the grain-size of a powder or the thickness of a film) is comparable to the intrinsic length scales of a superconductor such as the field penetration dcpth or the coherence length. The connection between the superconducting transition temperature (Tc) and particle size can be brought out from the simplified BCS equation: T c = 1.14 ®D exp (-I/N(0)V) (1) where ®D is the Debye temperature, N(0) is the electron density of states at the Fermi level and V is the electron-lattice interaction. A reduction in size has been found to lead to an increase in ®D [1], and is also expected [2] to enh~mce N(0), provided we consider the global density of states of an aggregate of particles. Both the factors would tend to raise T c (see Eqn. 1). In fact, a 75% increase in T c was observed on reducing the size of Atuminum particles to less than 150 ./k [3]. However, the study of size effects in oxide super- conductors is complicated by several factors. We have earlier studied [4] the superconducting and structural properties of YBa2Cu307.~ and Bi2Sr2CaCu2Os+y in the size range 75-300 nm. In either case, a decrease in size drives the crystal structure towards higher synmaetry by reducing the orthorhombic distortion. This structural change tended to reduce T c drastically. Increase in symmetry appears to be a general effect of size reduction [5]. Since a change towards higher symmetry (tetragonal structure) is known to favour superconductivity in La2.xSrxCuO4. 6, it is interesting to study size effects and consequent symmetry changes on the superconducting properties of this system. 2. Material synthesis Submicron Lal.ssSr0.15CuO4.~ (LSCO) was synthe- sized by a new liquid dehydration technique. The process involves a rapid nucleation of fine panicles of a mixture of the citrates of La, Sr and Cu from an aqueous stoichiometric solution. Acetone was used as dehydrating agent since it has a high solubility for water but not for the metal salts. The average panicle size of the product was detemfined by the initial solution concentration as well as the calcination temperature and time. Calcination at 750°C for 2 hours is sufficient to produce singlephase LSCO. Samples with different mean panicle sizes were produced by calcining at higher temperature. To ensure optimal uptake of oxygen, the samples were heated in flowing oxygen and slow cooled. The samples were characterized by x-ray diffraction (XRD), energy dispersive x-ray fluorescence (EDX), and scanning electron microscopy. Superconducting properties were studied by an ac-susceptometer and a SQUID magnetometer and the oxygen number (~5)measured by iodometric titration.