Biffed into Shape: BiFeO ₃ is known to have a very large ferroelectric polarization. Although the bulk ground state is rhombohedral (with the electrical polarization along the [111] direction), in thin films and under epitaxial strain, the material can be tetragonally distorted (polarization along [001]). Zeches et al. (p. 977 ) show that under compressive strain, these films are monoclinic, a phase that is highly stable because it comprises the same symmetry as the monoclinic phase which has been reported at the so-called morphotropic phase boundaries in technologically important ferroelectrics. This work offers the possibility of obtaining large piezoelectric responses in lead-free systems.

With the ability to engineer ferroelectricity in HfO ₂ thin films, manufacturable and highly scaled MFM capacitors and MFIS-FETs can be implemented into a CMOS-environment. NVM properties of the resulting devices are discussed and contrasted to existing perovskite based FRAM.

Biaxial strain is known to induce ferroelectricity in thin films of nominally nonferroelectric materials such as ${\mathrm{SrTiO}}_3$. By a direct comparison of the strained and strain-free ${\mathrm{SrTiO}}_3$ films using dielectric, ferroelectric, Raman, nonlinear optical and nanoscale piezoelectric property measurements, we conclude that all ${\mathrm{SrTiO}}_3$ films and bulk crystals are relaxor ferroelectrics, and the role of strain is to stabilize longer-range correlation of preexisting nanopolar regions, likely originating from minute amounts of unintentional Sr deficiency in nominally stoichiometric samples. These findings highlight the sensitive role of stoichiometry when exploring strain and epitaxy-induced electronic phenomena in oxide films, heterostructures, and interfaces.

Using spectroscopic ellipsometry, the room temperature refractive index and absorption versus wavelength of the ferroelectric antiferromagnet bismuth ferrite, $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ , are reported. The material has a direct band gap at $442\mathrm{nm}$ wavelength $\left(2.81\mathrm{eV}\right)$ . Using optical second harmonic generation, the nonlinear optical coefficients were determined to be $d_{15}∕d_{22}=0.20\pm 0.01$ , $d_{31}∕d_{22}=0.35\pm 0.02$ , $d_{33}∕d_{22}=-11.4\pm 0.20$ , and $\mid d_{22}\mid =298.4\pm 6.1\mathrm{pm}∕\mathrm{V}$ at a fundamental wavelength of $800\mathrm{nm}$ .