Structure and origin of polar nanoregions in relaxor ferroelectrics
In plain words
In relaxors such as lead magnesium niobate, the dipoles never line up into large domains; instead small polar patches, called polar nanoregions, appear and slow down on cooling. What these patches are and why they form is still argued.
Precise statement
In Pb(Mg1/3Nb2/3)O3 (PMN) and $\mathrm{PMN}-x\mathrm{PbTiO3}$, diffuse scattering and frequency-dispersive dielectric response (Vogel-Fulcher freezing near approximately 220 K in PMN) indicate polar correlations below a Burns temperature of approximately 600 K. Determine their structure (size distribution and correlation length versus $T$; discrete nanoregions versus a continuous slush of nanodomains) and their cause (random electric fields from B-site charge disorder, random bonds, or local strain) with a first-principles-based effective Hamiltonian validated against diffuse-scattering line shapes. An answer is a model reproducing the diffuse scattering and dielectric dispersion.
What would settle it
An atomistic model whose computed diffuse scattering and dielectric spectra match single-crystal data over 100 to 700 K without fitted correlation parameters.