摘要: Publisher Summary This chapter discusses valence changes in rare earth compounds under the influence of pressure, substitution, and temperature also some theoretical ideas that are currently vogue. The experimental aspects mainly monochalcogenides have been reviewed by Jayaraman et al ., Varma, Campagna Suryanarayanan. Some other materials known to exhibit fluctuations discussed along with monochalcogenides, these include SmB 6 , EUCu 2 Si 2. Among compounds, has earned certain notoriety as a system exhibiting change state; Sm ions higher state at room but toward lower upon lowering temperature. A number alloys involving Ce, Sm, Eu, Yb disilicides ( EuM ) where M is Fe, Cu or Ag, undergo ambient pressure fluctuating state.