Trends in negative thermal expansion behavior for AMO{sub 2} (A=Cu or Ag; M=Al, Sc, In, or La) compounds with the delafossite structure

Powder neutron diffraction data were obtained from 30 to 600K for CuAlO{sub 2}, CuInO{sub 2}, CuLaO{sub 2}, 2H CuScO{sub 2}, 3R CuScO{sub 2}, and AgInO{sub 2}. Rietveld refinements of these data showed negative thermal expansion (NTE) of the O-Cu-O linkage in all cases. This behavior was especially strong for CuLaO{sub 2} and CuScO{sub 2}, where it persisted up to our maximum measuring temperature of 600K. This NTE in turn caused NTE of the c cell edge, which was moderated by the positive thermal expansion of the M-O bonds. The NTE behavior increases in the CuMO{sub 2} series as the size of M increases. No NTE behavior was found for the O-Ag-O linkage in AgInO{sub 2}; nonetheless, this compound did exhibit NTE for the c cell edge at low temperatures. For CuLaO{sub 2} there is NTE for both the a and c cell edges at low temperatures. Structural trends for compounds with the delafossite structure are discussed with respect to both composition and temperature.