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Complex-oxide materials tuned to be near phase boundaries via chemistry/composition, temperature, pressure, etc. are known to exhibit large susceptibilities. Here, we observe a strain-driven nanoscale phase competition in epitaxially constrained Bi0.7La0.3FeO3 thin films near the antipolar-nonpolar phase boundary and explore the evolution of the structural, dielectric, (anti)ferroelectric, and magnetic properties with strain. We find that compressive and tensile strains can stabilize an antipolar PbZrO3-like Pbam phase and a nonpolar Pnma orthorhombic phase, respectively. Heterostructures grown with little to no strain exhibit a self-assembled nanoscale mixture of the two orthorhombic phases, wherein the relative fraction of each phase can be modified with film thickness. Subsequent investigation of the dielectric and (anti)ferroelectric properties reveals an electric-field-driven phase transformation from the nonpolar phase to the antipolar phase. X-ray linear dichroism reveals that the antiferromagnetic-spin axes can be effectively modified by the strain-induced phase transition. This evolution of antiferromagnetic-spin axes can be leveraged in exchange coupling between the antiferromagnetic Bi0.7La0.3FeO3 and a ferromagnetic Co0.9Fe0.1 layer to tune the ferromagnetic easy axis of the Co0.9Fe0.1. These results demonstrate that besides chemical alloying, epitaxial strain is an alternative and effective way to modify subtle phase relations and tune physical properties in rare earth-alloyed BiFeO3. Furthermore, the observation of antiferroelectric-antiferromagnetic properties in the Pbam Bi0.7La0.3FeO3 phase could be of significant scientific interest and great potential in magnetoelectric devices because of its dual antiferroic nature.

A strain-driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO3 thin films on silicon substrates. Biaxial compressive epitaxial strain is found to stabilize the rhombohedral phase at La concentrations beyond the morphotropic phase boundary (MPB). By tailoring the residual strain with film thickness, we demonstrate a mixed O/R phase structure consisting of O phase domains measuring tens of nanometers wide within a predominant R phase matrix. A combination of piezoresponse force microscopy (PFM), transmission electron microscopy (TEM), polarization–electric field hysteresis loop (P–E loop), and polarization maps reveal that the O-R structural change is an antiferroelectric to ferroelectric (AFE-FE) phase transition. Using scanning transmission electron microscopy (STEM), an atomically sharp O/R MPB is observed. Moreover, X-ray absorption spectra (XAS) and X-ray linear dichroism (XLD) measurements reveal a change in the antiferromagnetic axis orientation from out of plane...

Antiferroelectric PbZrO3 is being considered for a wide range of applications where the competition between centrosymmetric and noncentrosymmetric phases is important to the response. Here, we focus on the epitaxial growth of PbZrO3 thin films and understanding the chemistry–structure coupling in Pb1+δZrO3 (δ = 0, 0.1, 0.2). High-quality, single-phase Pb1+δZrO3 films are synthesized via pulsed-laser deposition. Although no significant lattice parameter change is observed in X-ray studies, electrical characterization reveals that while the PbZrO3 and Pb1.1ZrO3 heterostructures remain intrinsically antiferroelectric, the Pb1.2ZrO3 heterostructures exhibit a hysteresis loop indicative of ferroelectric response. Further X-ray scattering studies reveal strong quarter-order diffraction peaks in PbZrO3 and Pb1.1ZrO3 heterostructures indicative of antiferroelectricity, while no such peaks are observed for Pb1.2ZrO3 heterostructures. Density functional theory calculations suggest the large cation nonstoichiometry ...

We explore the effect of growth conditions on the cation and anion chemistry, electrical leakage, conduction mechanisms, and ferroelectric and dielectric behavior of BiFeO3. Although it is possible to produce single-phase, coherently strained films in all cases, small variations in the pulsed-laser deposition growth process, specifically the laser repetition rate and target composition, result in films with chemistries ranging from 10% Bi-deficiency to 4% Bi-excess and films possessing Bi gradients as large a 6% across the film thickness. Corresponding variations and gradients in the O chemistry are also observed. As a result of the varying film chemistry, marked differences in surface and domain morphology are observed wherein Bi-deficiency stabilizes atomically smooth surfaces and ordered stripe domains. Subsequent investigation of the current–voltage response reveals large differences in leakage current density arising from changes in both the overall stoichiometry and gradients. In turn, the film stoi...

Three new lead oxide benzoates have been prepared solvothermally. In two polymorphs, 1 and 2, of Pb2O(C6H5COO)2, distorted Pb4O tetrahedra share edges to form helical ∞1[Pb2O] chains. Unprecedented among Pb4O-based structures, these motifs may be viewed as double helices of lead atoms surrounding the central oxygen atoms. Both right- and left-handed helices are included in each structure. Formation of the polymorphs was controlled through variation in synthetic conditions. Polymorph 1 crystallizes in the achiral, polar space group Fdd2. Polymorph 2, in P21, is a rare example of a kryptoracemate in which crystallographically independent chains of both chiralities occur in the asymmetric unit. This second polymorph is both chiral and polar, and the pseudosymmetric relationship between the helices has been examined. In Pb4O(C6H5COO)6 (3), discrete Pb4O tetrahedra are bridged by benzoate ligands to form a one-dimensional hybrid structure. The compounds have been further characterized via IR spectroscopy, elem...