Abstract:
La[inf 2]CuO[inf 4] undergoes a structural phase transition from tetragonal to orthorhombic crystal symmetry as it is cooled below 525 K. Hole-doping the material (for example, by substituting Sr for La or Li for Cu) rapidly suppresses the structural transition temperature. Additionally, the in-plane lattice constant of La[inf 2-x]Sr[inf x]Cu[inf 1-y]Li[inf y]O[inf 4] is a function only of the combined hole count (i.e., x+y) and not of the individual Sr and Li concentrations. RUS measurements for stoichiometric, Sr-doped, and Li-doped La[inf 2]CuO[inf 4] have been used not only to map out the phase diagram of this system but also to reveal the unconventional nature of the transition. These results suggest a strong coupling between hole concentration and structural properties as well as a large in-plane/out-of-plane anisotropy.