  We report the investigations of crystal structure, electrical resistivity,
magnetization, specific heat, thermal conductivity, and thermoelectric power
(TEP) on La0.7Sr0.3(Mn1-xRux)O3 (LSMRO) compounds with x = 0 to 0.90. From the
analyses of crystal structure and magnetization measurements, it is inferred
that Ru should have a mixed valence of Ru3+ and Ru4+ for LSMRO with low level
of Ru substitution, and an additional mixed valence of Ru4+ and Ru5+ with
higher Ru substitution. It is found that all measured physical properties
undergo pronounced anomalies due to the ferromagnetic-paramagnetic phase
transition, and the observed transport properties of LSMRO can be reasonably
understood from the viewpoint of polaronic transport. The Curie temperatures TC
determined from the magnetization measurements are consistently higher than
those of the metal-insulator transitions TMI determined from the transport
measurements. By replacing Mn with Ru, both TC and TMI decrease concurrently
and the studied materials are driven toward the insulating phase with larger
value of x. It is also found that the entropy change during the phase
transition is reduced with more Ru substitution. These observations indicate
that the existence of Ru has the effect of weakening the ferromagnetism and
metallicity of the LSMRO perovskites.
