Domain boundary engineering investigates functionalities of twin boundaries and other interfaces and develops systems where such boundaries can be used as memory devices and active elements in nano-scale systems. The required functionalities include superconductivity, magnetism and ferroelectricity while the bulk has none of these properties. Superconducting twin walls were found in WO3 and ferrielectricity in CaTiO3. The novel method of 'resonant piezoelectric spectroscopy', RPS, revealed polar resonances in PST in its paraelectric phase and in paraelectric SrTiO3 at temperatures below 80 K. In SrTiO3 the resonances become strong at T < 40 K, they are induced by weak electric fields and lead to standing mechanical waves in the sample. This confirms the existence of structural phase transitions inside twin boundaries.
Any application of functional domain boundaries needs to deal with their dynamical response under high-frequency applied fields. We show that jamming leads to jerks and avalanche dynamics with power law dynamics over several decades. Materials with strong elastic interactions (such as collapsing porous ceramics from the Krieven group) show avalanche dynamics over several decades and exponents close to mean field values. The high temperature behavior with Vogel-Fulcher dynamics is now understood as a superposition of a-thermal avalanches in the yield regime and thermally excited jerks in the plastic regime. Detailed results of large scale computer simulations will be discussed and compared with analytical predictions.