J O U R N A L O F C H E M I S T R Y Materials Low temperature synthesis, structure and properties of La4BaCu5-xMxO13+d (M=Ni, Co and Fe)† C. Shivakumara,a M. S. Hegde,*a K. Sooryanarayana,a T. N. Guru Rowa and G. N. Subbannab aSolid State and Structural Chemistry Unit, and bMaterial Research Centre, Indian Institute of Science, Bangalore-560 012, India. E-mail: mshegde@sscu.iisc.ernet.in Received 8th June 1998, Accepted 9th September 1998 Oxygen deficient defect perovskite oxides having the general formula La4BaCu5-xMxO13+d (M=Ni or Co, 0x1.0, Fe, x=0.5) have been synthesized from NaOH–KOH fluxes at 450 °C.Structures of these materials have been refined by the Rietveld method and confirmed by electron diVraction studies. Ni3+, Co3+ and Fe3+ ions are shown to occupy the octahedral 1(a) site in the La4BaCu5O13+d structure.While the Ni substituted compound is metallic, composition controlled metal to insulator (M–I ) like behaviour is observed for Co and Fe substituted compounds. While temperature independent magnetic susceptibility in the case of the Ni substituted compound indicated Pauli paramagnetic behaviour, Co and Fe substituted oxides were weakly paramagnetic. 0x1, Fe, x0.5) and here we report their low temperature Introduction synthesis, structure and properties. Among the new families of copper oxides discovered since the outbreak of superconductivity studies in 1986,1 La4BaCu5O13+d2 is unique because it shows metallic behaviour Experimental down to lowest possible temperatures without undergoing a Stoichiometric amounts of high purity La2O3, CuO, NiO, superconducting transition.LaCuO33 is another oxide which Co3O4, Fe(C2O4)·2H2O and an excess of Ba(OH)2·8H2O were shows metallic properties and no superconductivity. Otherground in an agate mortar and added to a preheated 151 melt wise, families of copper oxides such as La2-xSrxCuO4, of NaOH and KOH (AR grade) at 400 °C in a recrystallized YBa2Cu3O7-d , and Bi2Sr2Can-1CunO2n+4+d (n=1, 2, 3) alumina crucible.A typical run contained La2O3 (1.3032 g), etc., show metallic and superconducting behaviour.4–6 CuO (0.7954 g), Ba(OH)2·8H2O (2.52 g), NaOH (10 g) and La4BaCu5O13+d crystallizes in a tetragonal structure in the KOH (10 g) and led to a product La4BaCu5O13.14. The space group P4/m, which is related to cubic perovskite subcell temperature was increased and held at 450 °C for 2–4 days.by a#ap Ó5=8.65 A° and c=ap=3.86 A° . The model structure7 Initially a clear blue solution was observed and gradually dark consists of groups of corner sharing CuO5 pyramids linked crystals precipitated. The melt was furnace cooled to room through CuO6 octahedra in such a way that each octahedron temperature, washed with distilled water followed by acetone shares four corners with four pyramids and two corners with and dried at 120 °C for 4 h.Powder X-ray diVraction patterns two octahedra and each pyramid is connected to four other were recorded on a JEOL JDX-8P diVractometer, with a scan pyramids and one octahedron. While substitution for the La speed of 2° min-1 with a Cu-Ka (l=1.5418 A° ; Ni filter) source site in this system has been performed by Vijayaraghavan to identify the phases.The structural parameters of some of et al.,8 to the best of our knowledge, no substitution for Cu these phases were refined by Rietveld profile analysis with the has been reported in the literature. diVraction data collected on a STOE STADI/P diVractometer. Superconducting oxides having the formula The data were collected using a linear position sensitive La2-xMxCuO4(M=Na, K),9 pyrochlore related oxides detector (PSD) in the range of 5<2h/°<80 in steps of 0.02° A2BB¾O7 (A=La or Nd; BB¾=Pb, Sn or Bi)10 and in the transmission mode.The morphology and composition RBa2Cu3O7-d (R=Nd, Sm, Eu or Gd)11 have been syntheof these crystalline phases were obtained from scanning elec- sized at low temperature by the NaOH–KOH flux method; tron microscopy (SEM) and energy dispersive X-ray (EDX) however, LaBa2Cu3O7-d could not be synthesized by this analysis. Oxygen content was determined by iodometric method.It is known that partial substitution of Ni for Cu in titration and thermogravimetric analysis (TGA) by heating YBa2Cu3O7 occurs with Ni2+ occupying Cu(2) sites.12 the sample under a stream of 15% H2–85% Ar.Electron However, by partial substitution of Ni for Cu in LaBa2Cu3O7, microscopy studies were carried out on as-synthesized samples Ni3+ ions were shown to occupy the Cu(1) sites.13 Also, to confirm the structure using a JEOL 200-CX transmission LaBa2Cu3-xNixO7+d (x0.3) showed metallic behaviour.In electron microscope. The polycrystalline powder was pelletised an attempt to synthesize the LaBa2Cu3O7-d phase by a low and sintered at 900 °C. No detectable change in the structure temperature route employing NaOH–KOH flux, we found was observed in any of the samples. Further, a temperature that a thermodynamically stable La4BaCu5O13+d phase was programmed desorption (TPD) system attached to a VG obtained.In the La4BaCu5O13+d phase, out of five Cu, one QXK-300 quadrupole mass spectrometer showed no evolution Cu has octahedral coordination and since Ni3+, Co3 + and of oxygen up to 750 °C indicating that there is no measurable Fe3+ ions prefer octahedral co-ordination, it was conceivable change in the oxygen content after sintering. Further, oxygen that one Cu can be substituted by these trivalent ions.Indeed estimation of the sample sintered at 750 °C and also at 900 °C we have synthesized La4BaCu5-xMxO13+d (M=Co or Ni, were carried out and no measurable changes in the total oxygen content were observed. Electrical resistivity measurements were carried out on the sintered pellets by a four-probe †Contribution No. 1338 from Solid State and Structural Chemistry Unit.method in the temperature range 300–15 K. dc Magnetic J. Mater. Chem., 1998, 8, 2695–2700 2695susceptibility measurements have been performed in the range 300–20 K employing a Lewis coil force magnetometer (George Associates, Model 2000). Results and discussion Synthesis and structure In an attempt to obtain the LaBa2Cu2NiO7+d phase by a low temperature method, stoichiometric amounts of La2O3, CuO and NiO with an excess of Ba(OH)2·8H2O were melted in an NaOH–KOH flux.The resulting crystalline material on examination by X-ray powder diVraction, electron microscopy and energy dispersive X-ray (EDX) analysis showed the presence of hexagonal BaNiO2+d and CuO, in addition to an unknown phase. Formation of BaNiO2+d in an alkali flux is known.14 Therefore it was clear that almost all of the Ni in the melt formed a BaNiO2+d phase.A composition corresponding to LaBa2Cu3O7 was heated in the flux with the absence of Ni in the melt. The powder XRD data of the resulting product revealed the formation of the same unknown phase and CuO as an impurity. On careful examination of several crystals in spot mode by EDX, compositions of La5Ba5Cu was found to be 45155 in the unknown phase indicating the possibility of La4BaCu5O13+d oxide formation.Then, the composition corresponding to La4BaCu5O13+d was heated in the flux and the powder X-ray diVraction pattern of this compound is shown in Fig. 1(a). All the lines could be indexed to the La4BaCu5O13+d phase. The lattice parameters agreed well with those reported in the literature.7 Mixed oxides La4BaCu5-xNixO13+d (0x1.0) were then synthesized by taking stoichiometric amounts of La2O3, CuO and NiO with an excess of Ba(OH)2·8H2O. An X-ray powder diVraction pattern for x=1.0 is shown in Fig. 1(b). As can Fig. 2 Scanning electron micrographs of (a) La4BaCu5O13.14 and be seen, all the lines could be indexed to the parent phase.In (b) La4BaCu4CoO13.35. an attempt to substitute Ni to >1 atom per formula unit, compounds were prepared for composition La4BaCu4-xNi1+xO13+d. However, the resulting products did not crystallize in the La4BaCu5O13+d structure. Mixed oxides La4BaCu5-xCoxO13+d (0x 1) were also synthesized and the pattern for x=1 is shown in Fig. 1(c). In the case of Fe, a value of x up to 0.5 could be substituted.For x>0.5, LaFeO3 impurity phase was observed in the Xray pattern in addition to Fe substituted La4BaCu5O13+d. DiVraction patterns for x=0.5 and 1.0 are shown in Fig. 1(d) and (e), respectively. Scanning electron micrographs of La4BaCu5O13+d, and the Ni, Co and Fe substituted samples showed a cuboidal morphology. Crystals of size 0.1–0.2 mm were seen in these preparations.Typical scanning electron micrographs of the Fig. 1 Powder X-ray diVraction patterns of (a) La4BaCu5O13.14 (b) Fig. 3 Thermogravimetric analysis curves for (a) La4BaCu5O13.14 and La4BaCu4NiO13.20, (c) La4BaCu4CoO13.35, (d) La4BaCu4.5Fe0.5O13.28 and (e) La4BaCu4FeO13+d (asterisk indicates LaFeO3 impurity phase). (b) La4BaCu4CoO13.35. 2696 J. Mater. Chem., 1998, 8, 2695–2700Table 1 Compounds, lattice parameters and oxygen contents Table 2 Crystallographic and structural refinement data for La4BaCu4NiO13.20 and La4BaCu4CoO13.35 Lattice parameter/A° Oxygen contenta Empirical formula La4BaCu4NiO13.20 La4BaCu4CoO13.35 Crystal system Tetragonal Tetragonal Compound a c Iodometryb TGAc Space group P4/m P4/m Unit cell dimensions/A° a=8.6820(1) a=8.6790(1) La4BaCu5O13+d 8.668(3) 3.862(5) 13.14 13.23 La4BaCu4NiO13+d 8.682(1) 3.869(6) 13.20 — c=3.8699(6) c=3.8731(6) Volume/A° 3 291.69 291.72 La4BaCu4CoO13+d 8.679(1) 3.873(6) 13.35 13.29 La4BaCu4.5Fe0.5O13+d 8.673(3) 3.866(5) 13.28 13.25 Z 1.00 1.00 F(000) 533.8 532.6 aIn atoms per formula unit.bValues accurate to within ±0.02. cValues Dc/g cm-3 6.952 6.983 accurate to within ±0.03.Radiation (l/A° ) Cu-Ka1 (1.540 56) Cu-Ka1 (1.540 56) DiVractometer STOE STADI/P STOE STADI/P DiVraction mode Transmission Transmission Measurement method 2h–v 2h–v parent and the Co substituted samples are shown in Fig. 2(a) 2h° (begin, end, step) 5.0, 79.94, 0.02 5.0, 79.94, 0.02 and (b). EDX analysis in spot mode was performed on each 2h zero point -0.1236 -0.1182 of these samples.Results showed that the metal ions were Absorption correction Empirical Empirical within 3% of the formula corresponding to La4BaCu4MO13+d Refinement method Refinement F2 Refinement F2 (M=Ni, Co) and La4BaCu4.5Fe0.5O13+d. Profile function Pearson VII with Pearson VII with Thermogravimetric analysis curves for La4BaCu5O13+d and exponent 2.00 exponent 2.00 R(1. hkl) 0.130 0.150 for the Co substituted sample are shown in Fig. 3. The TGA Rp 0.085 0.063 products contained La2O3, BaO and Cu as identified by XRwp 0.108 0.080 ray diVraction. For Co and Ni substituted compounds, Cu, Co and Ni metal peaks could be detected in addition to La2O3 and BaO. Oxygen estimation was also determined by iodo- Table 3 Selected bond lengths (A° ) for La4BaCu4NiO13.20 and metric titration.Oxygen content as determined by thermo- La4BaCu4CoO13.35 gravimetric analysis as well as iodometric titration and the lattice parameters are summarized in Table 1. La4BaCu4NiO13.20 La4BaCu4CoO13.35 Having confirmed the compositions of these phases, powder NiMO1×2 1.935(3) CoMO1×2 1.937(3) X-ray diVraction patterns were recorded for Rietveld analysis.NiMO4×4 1.932(33) CoMO4×4 1.973(23) Fig. 4 shows the observed, calculated and diVerence X-ray CuMO2×1 1.721(41) CuMO2×1 1.707(44) diVraction patterns for the La4BaCu4CoO13.35 phase. CuMO3×1 2.156(20) CuMO3×1 2.235(19) Refinements were performed keeping Co in the octahedral site CuMO3¾×1 2.076(10) CuMO3¾×1 1.931(20) fully occupied and also allowing it to mix with the other CuMO4×1 1.833(23) CuMO4×1 1.870(23) CuMO5×2 1.951(25) CuMO5×2 1.944(20) allowed sites of copper.The refinements with Co in the BaMO3×8 2.844(15) BaMO3×8 2.861(15) octahedral site gave the best fit as indicated by the R factors BaMO5×4 2.903(16) BaMO5×4 3.056(20) given in Table 2. For La4BaCu4NiO13.20 also, the structure LaMO1×1 2.670(20) LaMO1×1 2.643(18) was refined with Ni3+ in the 1(a) site similarly to the Co case LaMO2×2 2.905(16) LaMO2×2 2.940(18) and the final R factors are good. Mixing of Ni ions in Cu sites LaMO3×2 2.582(13) LaMO3×2 2.576(13) either fully or partially did not show any significant increase LaMO4×2 2.749(14) LaMO4×2 2.671(18) LaMO4¾×2 2.659(13) LaMO4¾×2 2.717(16) in R factors because of nearly similar scattering factors.LaMO5×1 2.859(17) LaMO5×1 2.758(20) Therefore, occupation of Ni3+ solely in the 1(a) position could LaMO5¾×1 2.565(19) LaMO5¾×1 2.738(20) not be ascertained.However, Ni3+ is known to prefer six co- LaMO5×1 2.808(19) LaMO5×1 2.648(20) ordination in perovskite related oxides such as LaNiO3. It may be noted that La4BaCu4-xNi1+xO13+d does not crystallize in the parent structure. Therefore it is reasonable to expect Table 4 Fractional atomic coordinates and isotropic thermal Ni3+ ions to occupy the 1(a) position with six co-ordination parameters (A° 2) for La4BaCu4NiO13.20 and La4BaCu4CoO13.35 while four Cu ions occupy 4( j) positions with five coordi- La4BaCu4NiO13.20 nation.Details of the refinement with Ni in the 1(a) site are given in Table 2. Selected bond lengths for La4BaCu4NiO13.20 Atom x y z Uiso and La4BaCu4CoO13.35 are given in Table 3 and fractional La 0.1221(22) 0.2823(27) 0.50000 0.020(14) Ba 0.50000 0.50000 0.50000 0.030(1) Ni 0.00000 0.00000 0.00000 0.022(6) Cu 0.3988(50) 0.1705(38) 0.00000 0.022(6) O1 0.00000 0.00000 0.50000 0.05000 O2 0.00000 0.50000 0.00000 0.05000 O3 0.2858(251) 0.3917(205) 0.00000 0.05000 O4 0.2041(279) 0.0888(224) 0.00000 0.05000 O5 0.4268(230) 0.1738(189) 0.50000 0.05000 La4BaCu4CoO13.35 Atom x y z Uiso La 0.1248(25) 0.2778(28) 0.50000 0.018(4) Ba 0.50000 0.50000 0.50000 0.050(2) Cu 0.4073(52) 0.1735(51) 0.00000 0.018(8) Co 0.00000 0.00000 0.00000 0.018(8) O1 0.00000 0.00000 0.50000 0.05000 O2 0.00000 0.50000 0.00000 0.05000 O3 0.2801(242) 0.3974(196) 0.00000 0.05000 O4 0.2111(262) 0.0843(311) 0.00000 0.05000 Fig. 4 Observed, calculated and diVerence powder X-ray patterns for O5 0.4188(236) 0.1574(219) 0.50000 0.05000 La4BaCu4CoO13.35. J. Mater. Chem., 1998, 8, 2695–2700 2697atomic coordinates and isotropic thermal parameters are given correspond to the ‘a’ parameter of the unit cell. The inset shows the corresponding diVraction pattern. Thus, electron in Table 4. Full Crystallographic details, excluding structure factors, microscopic studies confirm the formation of La4BaCu5O13+d, and the Ni and Co substituted phases by our low have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Information for Authors, J. Mater. temperature route. Synthesis of these oxides using a low temperature Chem., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the NaOH–KOH flux is important, because, Ni, Co and Fe substituted compounds cannot be synthesized by a solid state reference number 1145/117. Selected area electron diVraction patterns were recorded on route.Substitution of both Co and Ni up to one atom per formula unit has been achieved. several crystallites, to confirm the formation of the La4BaCu5O13.14 phase.Fig. 5(a) and (b) show the electron diVraction patterns of the parent phase recorded along (001) Electrical and magnetic properties and (010) zone axes. Lattice parameters obtained here agree well with the X-ray results and those reported in the literature.7 Fig. 6(a) shows plots of electrical resistivity vs. temperature between 300 and 15 K for La4BaCu5O13.14, La4BaCu4NiO13.20 The electron diVraction pattern of the Ni substituted oxide La4BaCu4NiO13.20 is shown in Fig. 5(c) recorded along the and La4BaCu4CoO13.35. The parent and the Ni substituted phases showed metallic behaviour. La4BaCu5-xNixO13+d (x= (001) zone axis. High resolution images were also recorded on the parent as well as Ni and Co substituted oxides.Fig. 5(d) 0.25, 0.50) were also synthesized and these compounds also showed metallic behaviour, while the La4BaCu4CoO13.35 oxide shows the high resolution image recorded along (010) for the Co substituted oxide. Observed lattice fringes of ca. 8.65 A° showed semiconducting like behaviour. It is important to note Fig. 5 Selected area electron diVraction patterns of La4BaCu5O13.14 in (a) (001) and (b) (010) zone axes; SAED of La4BaCu4NiO13.20 in (c) (001) zone axis and (d) high resolution image of La4BaCu4CoO13.35 showing ca. 8.65 A° periodicity; inset shows corresponding diVraction pattern recorded along the (010) axis. 2698 J. Mater. Chem., 1998, 8, 2695–2700Fig. 8 Resistivity vs. temperature curve for La4BaCu4.5Fe0.5O13.28. In inset susceptibility vs.temperature plot is given. The susceptibility value of the Co containing phase was higher at 300 K and nearly temperature independent and weak paramagnetic like behaviour was observed as the sample is cooled which did not follow the Curie law. As the Co content was increased, the susceptibility at 300 K increased from 3×10-6 to 18×10-6 emu g-1 from x=0 to 1.0. The susceptibility x was fitted to a function (C/T)+a, where a is a temperature independent contribution. For La4BaCu5-xCoxO13+d, magnetic moments were 0.3, 0.8 and 1.0 mB for x=0, 0.5 and 1.0, respectively, per formula unit.The low value of 0.06 mB per Cu is characteristic of delocalized carriers.2 If Co3+ ions in this compound are in high spin state, the expected moment is 4.7 mB, even assuming that the magnetic moment solely arises from Co in La4BaCu4CoO13.35.The low Fig. 6 Resistivity as a function of temperature curves for value of 1.0 mB observed here suggests that the spins on Co (a) La4BaCu5-xMxO13+d and (b) La4BaCu5-xCoxO13+d. are not fully localized. Fig. 8 shows the resistivity vs. temperature plot of that the resistivity of La4BaCu4CoO13.35 at 300 K is of the La4BaCu4.5Fe0.5O13.28. The oxide showed metallic behaviour same order of magnitude as that of the parent as well as from 300 to 100 K and started showing semiconducting like the Ni substituted oxides.Fig. 6(b) shows resistivity vs. tem- behaviour below 100 K. In the inset the susceptibility as a perature plots of La4BaCu5-xCoxO13+d (0x1.0). For x= function of temperature is shown.The results reveal that the 0.5, the compound is still metallic and for x>0.5, semiconduct- Fe doped compound exhibits weakly paramagnetic behaviour. ing like behaviour is observed. Thus, the Co doped oxide Metallic behaviour in La4BaCu5O13.14 is due to complete shows composition controlled metal to insulating like overlap of Cu 3d and O 2p bands. The average oxidation state behaviour as the cobalt content increased from 0 to 1.of Cu in this compound is 2.45. This can be represented by Magnetic susceptibility vs. temperature plots of the equilibrium:15 La4BaCu5O13.14, La4 BaCu4NiO13.20, La4BaCu4.5Co0.5O13+d Cu3++O2-=Cu2++O1- (1) and La4BaCu4CoO13.35 are shown in Fig. 7. Both Cu and Ni phases showed temperature independent susceptibility from This indicates the presence of holes on copper as well as 300 to 20 K.oxygen. The Ni, Co and Fe substituted oxides are made under highly oxidizing conditions and these metal ions should be in the +3 state. This follows from the fact that LaNiO3, LaCoO3 and LaFeO3 can be synthesized from NaOH–KOH flux at 450 °C. Thus, with Ni3+ in La4BaCu4NiO13.2, the average oxidation number of Cu is 2.35.Accordingly, the hole concentration on Cu is high as indicated by equilibrium (1). As in LaNiO3, Ni3+ in this compound is in octahedral coordination. Since LaNiO3 itself is a metallic and Pauli paramagnetic oxide, metallic and Pauli paramagnetic behaviour is expected for La4BaCu4NiO13.2. A similar situation exists in LaBa2Cu3-xNixO7+d (0.1x0.3),13 where Ni occupies the Cu(1) sites in the +3 state and the compounds are metallic down to 15 K.The cobalt substituted compound, La4BaCu4CoO13.35, shows semiconducting behaviour. Assuming Co in the +3 oxidation state, the average oxidation state of Cu is 2.42. Therefore, equilibrium (1) should exist in this compound. Since, oxidation of Co3+ to Co4+ is more facile than Cu2+ to Cu3+, it is possible to consider additional electron exchange Fig. 7 Magnetic susceptibility as a function of temperature curves for via oxygen as follows: (a) La4BaCu5O13.14, (b) La4BaCu4NiO13.20, (c) La4BaCu4.5Co0.5O13+d and (d) La4BaCu4CoO13.35. Cu3++Co3+=Cu2++Co4+ (2) J. Mater. Chem., 1998, 8, 2695–2700 2699A similar situation exists in LaBa2Cu2CoO7.35 which also References shows semiconducting behaviour.16 It should be noted that 1 J.G. Bednorz and K. A. Muller, Z. Phys. B, 1986, 64, 189. LaCoO3 is semiconducting and the presence of Co3+ or excess 2 C. Michel, L. Er-Rakho and B. Raveau, Mater. Res. Bull., 1985, of Cu2+ by equilibrium (2) would lead to a semiconducting 20, 667. behaviour in this compound. A fairly high conductivity at 3 G. Demazeau, C. Parent, M. Pouchard and P. Hagenmuller, 300K in La4 BaCu4CoO13.35 can be attributed to the high Mater. Res.Bull., 1972, 7, 913: J. B.Goodenough, N. F. Mott, oxidation number of Cu (2.42) or equivalently, high M. Pouchard, G. Demazeau and P. Hagenmuller, Mater. Res. Bull., 1973, 8, 647. concentration of holes. 4 R. J. Cava, R. B. Van Dover, B. Batlogg and E. A. Rietman, Phys. For the Fe substituted oxide, even at x=0.5, the compound Rev.Lett., 1987, 58, 408. exhibits semiconducting behaviour below 100 K. Here also, 5 M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang and C. W. Chu, Phys. Rev. Cu3++Fe3+=Cu2++Fe4+ (3) Lett., 1987, 58, 908. 6 M. Maeda, Y. Tanaka, M. Fukutomi and A. Asano, Jpn. J. Appl. equilibrium can occur as is seen in La2-xSrxCu1-yFeyO4.17 Phys., 1988, 27, L209.Unlike in the case of divalent ion doped LaCoO3 (e.g. 7 C.Michel, L. Er-Rakho, M. Herview, J. Pannetier and B. Raveau, La0.67Sr0.33CoO3) which is metallic, La1-xSrxFeO3 phases do J. Solid State Chem., 1987, 68, 143. not show metallic behaviour. Therefore, semiconducting 8 R. Vijayaraghavan, R. A. Mohan Ram and C. N. R. Rao, J. Solid State Chem., 1988, 78, 316.behaviour is expected for the Fe substituted compound even 9 W. K. Ham, G. F. Holland and A. M. Stacy, J. Am. Chem. Soc., for x=0.5. 1988, 110, 5214. 10 S. Uma and J. Gopalakrishnan, J. Solid State Chem., 1993, 105, 595. Conclusions 11 L. N. Marquez, S. W. Keller and A. M. Stacy, Chem. Mater., 1993, 5, 761. La4BaCu5O13.14 and Ni, Co and Fe substituted phases have 12 J. M. Tarascon, P. Barboux, P. F. Miceli, L. H. Greene, been synthesized by a low temperature route employing an G. W. Hull, M. Eibshutz and S. A. Sunshine, Phys. Rev. B, 1998, NaOH–KOH flux. While the parent La4BaCu5O13.14 and the 37, 7458. La4BaCu4NiO13.20 showed metallic and Pauli paramagnetic 13 S. Sundar Manoharan, S. Ramesh, M. S. Hegde and G. N. Subbanna, J. Solid State Chem., 1994, 112, 281. behaviour, Co and Fe substituted oxides show composition 14 J. DiCarlo, I. Yazdi, and A. J. Jacobson, J. Solid State Chem., controlled metal to insulator transitions and they are weakly 1994, 109, 223. paramagnetic. These observations are explained by possible 15 J. B. Goodenough and A. Manthiram, J. Solid State Chem., 1990, charge exchange between Co3+ and Fe3+ with Cu3+ via 88, 115. oxide ion. 16 S. Ramesh, N. Y. Vasanthacharya, M. S. Hegde, G. N. Subbanna, H. Rajagopal, A . Sequiera and S. K. Paranjpe, Physica C, 1995, 253, 243; S. Ramesh and M. S. Hegde, J. Phys. Chem., 1996, We thank Professor J. Gopalakrishnan for useful suggestions 100, 8443. and the Department of Science and Technology for financial 17 K. Ramesha, S. Uma, N. Y. Vasanthacharya and assistance. One of us (KS) thanks the Council of Scientific J. Gopalakrishnan, J. Solid State Chem., 1997, 128, 169. and Industrial Research (CSIR) for a senior research fellowship. Paper 8/04334E 2700 J. Mater. Chem., 1998, 8, 2695–2700