Synthesis and properties of Ba3NaRu2O9-δ and Ba3(Na, R)Ru2O9-δ (R=rare earth) crystals

Crystals of Ba3NaRu2O9-delta (deltaapproximate to0.5) and Ba-3(Na, R)Ru2O9-delta (R=Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6(3)mmc. Ba3NaRu2O9-delta and Ba-3(Na, R)Ru2O9-delta (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba3NaRu2O9-delta has an effective magnetic moment P-eff of 0.91 mu(B), while P-eff of Ba-3(Na, R)Ru2O9-delta (except Ce) reflects the large free-ion moment grootJ(J+ 1) of the rare earth ions. Ba-3(Na, Ce)Ru2O9-delta shows peculiar magnetic behavior that differs from the magnetism of other Ba-3(Na, R)Ru2O9-delta crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.1similar to0.2 eV. (C) 2002 Elsevier Science B.V. All rights reserved.