PREPARATION AND TRANSPORT-PROPERTIES OF NEW TERNARY TELLURIDES A(X)NB(6)TE(8) (A=TL, CA, SR, PA, LA, AND ND)

New ternary niobium tellurides A(x)Nb(6)Te(8) (A = Ca, Sr, Ba, La, and Nd; x = 0.22-0.32) have been prepared by molten salt ion exchange rea ctions of TlxNb6Te8 with rare earth/alkaline earth iodides AI(3)/AI(2) at relatively low temperatures, 535-795 degrees C. Most of the niobiu m tellurides show metallic behavior followed by superconductivity at l ow temperatures, 4-6 K. Polycrystalline La0.32Nb6Te8 and Nd0.24Nb6Te8 show a resistivity anomaly at 46 and 43 K, respectively, while polycry stalline Tl0.91Nb6Te8 shows a broad resistivity anomaly at 160-220 K. The resistivity anomaly observed in Tl0.91Nb6Te8 appears to be accompa nied by a minor structural distortion evidenced in differential scanni ng calorimetry. The resistivity anomalies observed in La0.32Nb6Te8 and Nd0.24Nb6Te8 are similar to those observed at similar to 40 K for Nb3 Te4 and may be related to the onset of a charge density wave type inst ability. (C) 1996 Academic Press, Inc.