Physiea C 235-240 (1994) 755-756 North-Holland PHYSICA Infrared and Transport Properties of the Layered Perovskite Related Oxide BasNb40~s and its Oxygen Deficient Phases S. Pagola ", N.E. Massa b, G. Polla °, G. Leyva °, and R.E. Carbonio" " INFIQC, Dpto. de Fisicoquimica, Fac. Cs. Quimicas, U.N.C., CC 61, 5016, C6rdoba, Argentina. b LANAIS en Espectroscopia 6ptica and QUINOR - Dpto. de Quimica and Dpto. de Fisica, U.N.L.P., CC 962, 1900, La Plata, Argentina. ° CNEA, Dpto. de Fisica, Av. del Libertador 8250, 1429, Buenos Aires, Argentina. BasNb40~., oxides were studied by infrared, electrical resistivity and thermogravimmetric analysis (TGA). FIR reflectivity, measurementsreveal a strong ionic compound that has well defined features in groups that we assign to oxygen stretching, bending and lattice phonons splitted by the lower symmetry of this layered compound. For the sample with x = 0.56, oxygen vacancies do not affect phonon b~ld profiles, indicating that carriers are not free enough to interact with longitudinal modes. Electrical resistivity vs. temperature measurements show that the oxygen deficient compounds, for low values of x, are small band gap semiconductors. Since the discovery of high-temperature superconductivity, perovskite related oxides have 0een extensively studied in order to understand its mechanism and search for new materials. Among these, the non copper ones are growing in interest. Cations with and ~ (n=3, 4, 5) configuration such as Ti(III), Nb(IV) or Ta(IV) all having s=l/2 spin state, are of particular interest. Among the niobium oxides, Li,,NbO2 and (Sq.x P-,, )NbzO6 where R is a lantanide, were reported to be superconducting [1,2]. BasNb40~5 is a layered perovskite related oxide [3L that can be prepared with Nb(IV) as BasNb40~3. /dl these characteristics make this compound a good candidate to search for new superconductors. BasNb40~s was obtained by heat treatment of the stoichiomellic mixture of BaCO3 and Nb205 at 1000°C in air. The oxygen deficient phases were prepared by reduction of BasNb40~5 in a 95% Ar + 5% H: atmosphere by changing the temperature between 1300 and 1500°C and the time of reduction betwee md 54 hours. Ele~. ,a~ resistivity measuremenls have been done by he four probe method, between 80 and 300 K. The samples were characterized by TGA on a Mettler TG 50 equipment, x values were determined by the mass gain measured in flowing O~ at 600 °C. X ray powder diffraction measurements were done in a Philips PW 3710 Diffractometer, ,and temperature dependent reflective measurements have 0921-4534/94/$07.00 © 1994 - Elsevier Science B,V. All rights reserved. SSDI 0921-4534(94)00941-4 been done with and interferometer Bruker 113V from 5,000 to 30 cm 4 , the samples were mounted on an Oxford DN 1754 cryostat. Figure 1 shows our preliminary reflectivity spectra of BasNb4Ol5 and BasN~4014.44 at 80 K. X-ray diffraction powder patterns correspond to the Ba~Nb4Ot5 phase [3]. i00 .............................. "~ 60 40 /~ 0 ~ . . . . . 1500 1000 500 0 Frequency (cm -1) Figure 1. IR reflectivity spectra in the phonon region of Ba~Nb4Ots (solid line) and BasNb4Ot4.44(dashed line), at 80 K. The oxidized sample has a typical white ionic insulator color, while in contrast, a lead like shine is the characteristic for the one treated in the reducing atmosphere. Our spectra confirms earlier X-ray data showing that this layered compo,md has a perovskite distorted lattice. Unscreened pi~onon features from 800 to 30 cm ~ are found in g~oups at four, at the same frequency positions of the room temperature three infrared active reflection bands of