Theoretical Study on the Ordered Structure in Lanthanum-Modified Lead Zirconate Titanate

The 1/2111-type ordered structure observed in lanthanum-modified lead zirconate titanate has been proved to be stable in the next-nearest-neighbor approximation by the eightpoint cluster variation method. The order parameter as a function of the composition of La³⁺ and lead vacancies and the order-disorder phase diagram have been obtained.