The drastic reduction in dimensions in thin films, together with the low crystallization temperatures used, normally results in a large reduction in the grain size. It has been reported that relaxor ferroelectric states are stabilized at room temperature for fine‐grained ceramics and films that behave as normal ferroelectrics for large grains. In this work, the effects of the grain size reduction on the relaxor characteristics are analyzed for a composition that is already a canonical relaxor with a nonergodic state at room temperature: (Bi0.5Na0.5)1‐xBaxTiO3 (BNBT). The comparison of the local polar ordering within BNBT grains studied with piezoresponse force microscopy on large‐grained ceramics and fine‐grained thin films shows that the development of stable long‐range ferroelectric order with the application of an electric field is hampered due to the small grain size of the grains. The ergodic character of the high‐temperature phase is thus stabilized at room temperature, following a similar mechanism as the one discussed for other noncanonical relaxors.

Secretaría de Estado de Investigación, Desarrollo e Innovación. Grant Numbers: MAT2013‐40489‐P, MAT2016‐76851‐R Ministerio de Educación, Cultura y Deporte. Grant Number: Formación de Personal Universitario (AP2012‐0639) FP7 Ideas: European Research Council. Grant Number: Initial Training Network “Nanomotion” (grant agr