SYNTHESES AND PHYSICAL-PROPERTIES OF PYROCHLORE-TYPE A2B2O7 (A=TL,Y, B=CR,MN)

Pyrochlore-type A2B2O7 (A=Tl,Y; B=Cr,Mn) were synthesized under conditions of elevated temperature and pressure up to 1100°C and 9GPa. Magnetic measurements indicate that the transition metals in the compounds are tetravalent and Tl2Mn2O7 is ferromagnetic with the Curie temperature at 117K. Electric measurements show that Tl2Mn2O7 is a semiconductor with a resistivity maximum at temperatures near the magnetic transition point but other compounds possess high resistivity of the order of 108Ω·cm. © 1979.