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Abstract Multiferroics are materials exhibiting the coexistence of ferroelectricity and ideally ferromagnetism. Unfortunately, most known magnetoelectric multiferroics combine ferroelectricity with antiferromagnetism or with weak ferromagnetism. Here, following previous theoretical predictions, we provide clear experimental indications that ferroelectricity can be induced by epitaxial tensile strain in the ferromagnetic simple binary oxide EuO. We investigate the ferroelectric phase transition using infrared reflectance spectroscopy, finding that the frequency of the soft optical phonon reduces with increasing tensile strain and decreasing temperature. We observe such a soft mode anomaly at 100 K in (EuO) 2 /(BaO) 2 superlattices grown epitaxially on (LaAlO 3 ) 0.29 -(SrAl 1/2 Ta 1/2 O 3 ) 0.71 substrates, which is a typical signature for a displacive ferroelectric phase transition. The EuO in this superlattice is nominally subjected to 6.4% biaxial tensile strain, i.e., 50% more than believed needed from previously published calculations. We interpret our results with new first-principles density functional calculations using a hybrid functional, which provides a better quantitative agreement with experiment than the previously used local-density approximation and generalized gradient approximation functionals. 

Abstract A single‐crystal specimen of rutile (titania) was flashed repetitively, while increasing the electric field after each cycle. As expected, the flash onset temperature continued to drop modestly at higher fields. However, when the field was increased from 400 to 450 V cm^–1, the flashed onset fell dramatically down to room temperature. We have investigated the electrical and optical properties of this room temperature flashed specimen (called SZ). The specimen was electronically conducting. Optical absorption spectroscopy revealed a narrow band of new energy levels that were generated just below the conduction band. The gap between the conduction band and this flash‐induced energy level agreed with the peak in the electroluminescence spectrum. Optical second harmonic generation (SHG) is reported. The flash‐on condition significantly lowered the SHG, which rebounded when the flash was turned off. This result suggests that the structure becomes more centrosymmetric in the state of flash, which may represent a disordered state of defects. The possibility of studying flash behavior at room temperature, without a furnace (as in SZ type specimens), opens a considerable simplification for in‐situ characterization of flash behavior. For example, a possible relationship between memristor physics and the flash phenomenon can be studied. 

PbTiO3-based ferroelectrics have impressive electroactive properties, originating from the Pb2+ 6s2 electron lone-pair, which cause large elastic distortion and electric polarization due to cooperative pseudo Jahn-Teller effect. Recently, tin-based perovskite oxide (SnTiO3) containing Sn2+ and a chemistry similar to that of the 6s2 lone-pair has been identified as a thermally stable, environmentally friendly substitute for PbTiO3-based ferroelectrics. However experimental attempts to stabilize Sn2+ on the A-site of perovskite ATiO3 have so far failed. In this work, we report on the growth of atomically smooth, epitaxial, and coherent Sn-alloyed SrTiO3 films on SrTiO3 (001) substrates using a hybrid molecular beam epitaxy approach. With increasing Sn concentration, the out-of-plane lattice parameter first increases in accordance with the Vegard’s law and then decreases for Sn(Sr+Ti+Sn) at. % ratio > 0.1 due to the incorporation of Sn2+ at the A-site. Using a combination of high-resolution X-ray photoelectron spectroscopy and density functional calculations, we show that while majority of Sn is on the B-site, there is a quantitatively unknown fraction of Sn being consistent with the A-site occupancy making SrTiO3 polar. A relaxor-like ferroelectric local distortion with monoclinic symmetry, induced by A-site Sn2+, was observed in Sn-doped SrTiO3 with Sn(Sr+Ti+Sn) at. % ratio = 0.1 using optical second harmonic generation measurements. The role of growth kinetics on the stability of Sn2+ in SrTiO3 is discussed. 

Abstract The local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg_1/3Nb_2/3O₃(PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg_2/3Nb_1/3)O₃and PbNbO₃, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO₃substrates using alternate target timed pulsed‐laser deposition of Pb(Mg_2/3Nb_1/3)O₃and PbNbO₃targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm⁻²at room temperature. Polarization–electric field hysteresis loops, Rayleigh data, and optical second‐harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature‐dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films. 

Abstract Solid‐oxide fuel/electrolyzer cells are limited by a dearth of electrolyte materials with low ohmic loss and an incomplete understanding of the structure–property relationships that would enable the rational design of better materials. Here, using epitaxial thin‐film growth, synchrotron radiation, impedance spectroscopy, and density‐functional theory, the impact of structural parameters (i.e., unit‐cell volume and octahedral rotations) on ionic conductivity is delineated in La_0.9Sr_0.1Ga_0.95Mg_0.05O_3–δ. As compared to the zero‐strain state, compressive strain reduces the unit‐cell volume while maintaining large octahedral rotations, resulting in a strong reduction of ionic conductivity, while tensile strain increases the unit‐cell volume while quenching octahedral rotations, resulting in a negligible effect on the ionic conductivity. Calculations reveal that larger unit‐cell volumes and octahedral rotations decrease migration barriers and create low‐energy migration pathways, respectively. The desired combination of large unit‐cell volume and octahedral rotations is normally contraindicated, but through the creation of superlattice structures both expanded unit‐cell volume and large octahedral rotations are experimentally realized, which result in an enhancement of the ionic conductivity. All told, the potential to tune ionic conductivity with structure alone by a factor of ≈2.5 at around 600 °C is observed, which sheds new light on the rational design of ion‐conducting perovskite electrolytes.