Variations in lattice parameters with annealing temperature for L-Pd 5Ce

Abstract

The lattice parameters of L-Pd 5Ce have been determined as a function of annealing temperature. L-Pd 5Ce has a one-dimensional long-period superstructure derived from L1 2, and the long periodic direction is along [110] of the L1 2 lattice. At 873 K, the distance between adjacent anti-phase boundaries, or the domain size, is almost exactly M≡3 in units of the lattice spacing of (110) planes of L1 2 (≡= co), and the crystal structure is Pmma with the lattice parameters a=0.5700 mn, b=0.4062 nm and c=3 co=0.8462 nm. The axes correspond to [110], [001] and [110] respectively of L1 2. When M is even, the space group of the structure is regarded as Bmmm for the above setting of the axes. As the annealing temperature is elevated to 973 K, the quantities a/2 1/2, b and 2 1/2c o, which correspond to the lattice dimensions of the pseudocubic lattice of L1 2, then have an identical value to one another. The variation in lattice parameters is explained in terms of a rapid increase in M associated with atomic disordering. The observed lattice parameters indicate that the averaged atomic volume varies less than 0.2%. The small variation cannot be a cause of the distinct dependence of electrical resistivity upon the annealing temperature.