Carrier-mediated control over the soft mode and ferroelectricity in BaTiO3

We calculate the effects of conduction band electrons (CBEs), introduced by doping or photoexcitation, on ferroelectricity and phonon dynamics ${\mathrm{BaTiO}}_{3}$ (BTO). show that CBEs destabilize ferroelectricity, which would lower Curie temperature coercive field, might help to improve speed efficiency with polarization domains can be switched in ferroelectric devices. frequencies ${A}_{1}$ soft modes BTO's phases, raise soft-mode frequency its paraelectric phase. also femtosecond laser pulses could used selectively excite a coherent ferroelectric-mode phonon. This allow this much-studied excitation monitored pump-probe spectroscopy as it decays into other modes. many properties doped undoped BTO have simple intuitive explanations, within an ionic picture bonding, if is assumed not driven long-range interactions, but attraction between Ti O neighbors. Most are consequences them reducing ions' charges increasing their polarizabilities, thereby weakening Ti-O attraction. As CBE density increases, so does delocalized interstitial electrons, increase conductivity. argue polar metallic phase exists threshold for conductivity reached before make distortions energetically unfavorable critically