J. B. Neaton

First-principles study of spontaneous polarization in multiferroic BiFeO 3

The ground-state structural and electronic properties of ferroelectric BiFeO 3 are calculated using density functional theory within the local spin-density approximation sLSDAd and the LSDA+U method. The crystal structure is computed to be rhombohedral with space group R3c, and the electronic structure is found to be insulating and antiferromagnetic, both in excellent agreement with available experiments. A large ferroelectric polarization of 90‐ 100 m C/c m 2 is predicted, consistent with the large atomic displacements in the ferroelectric phase and with recent experimental reports, but differing by an order of magnitude from early experiments. One possible explanation is that the latter may have suffered from large leakage currents. However, both past and contemporary measurements are shown to be consistent with the modern theory of polarization, suggesting that the range of reported polarizations may instead correspond to distinct switching paths in structural space. Modern measurements on well-characterized bulk samples are required to confirm this interpretation.

Extrinsic models for the dielectric response of CaCu3Ti4O12

The large, temperature-independent, low-frequency dielectric constant recently observed in single-crystal CaCu3Ti4O12 is most plausibly interpreted as arising from spatial inhomogenities of its local dielectric response. Probable sources of inhomogeneity are the various domain boundaries endemic in such materials: twin, Ca ordering, and antiphase boundaries. The material in, and neighboring, such boundaries can be insulating or conducting. We construct a decision tree for the resulting six possible morphologies, and derive or present expressions for the dielectric constant for models of each morphology. We conclude that all six morphologies can yield dielectric behavior consistent with observations. Thus, present experimental findings are insufficient to establish the internal morphology responsible for the remarkable properties of CaCu3Ti4O12, and we suggest further experiments to distinguish among them.

First-principles study of the structure and lattice dielectric response of CaCu 3 Ti 4 O 12

Structural and electronic properties of

Lattice dielectric response of CdCu 3 Ti 4 O 12 and CaCu 3 Ti 4 O 12 from first principles

{\mathrm{CaCu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}

First-principles study of adhesion at C u / S i O 2 interfaces

are calculated using density-functional theory within the local spin-density approximation. After an analysis of structural stability, zone-center optical phonon frequencies are evaluated using the frozen-phonon method and mode effective charges are determined from computed Berry-phase polarizations. Excellent agreement between calculated and measured phonon frequencies is obtained. The calculated mode effective charges are in poorer agreement with experiment, although they are of the correct order of magnitude and the lattice contribution to the static dielectric constant is calculated to be

Effective‐Hamiltonian Modeling of External Pressures in Ferroelectric Perovskites

\ensuremath{\sim}40.

Ab initio study of the phase diagram of epitaxial BaTiO 3

On the basis of these results, various mechanisms are considered for the enormous dielectric response reported in recent experiments. No direct evidence is found for intrinsic lattice or electronic mechanisms, suggesting that increased attention should be given to extrinsic effects.

Lattice dielectric response of CdCu3Ti4O12 and of CaCu3Ti4O12 from first principles

Structural, vibrational, and lattice dielectric properties of

Flat branches and pressure amorphization

{\mathrm{CdCu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}

Pressure amorphization through displacive disorder

are studied using the density-functional theory within the local spin-density approximation, and the results are compared with those computed previously for