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Recent advances in thin-fi lm engineering leads to a new type of mixed-phase system in BiFeO 3 (BFO) epitaxial fi lms driven by substrate strain. [ 1 ] Single-phase multiferroic BFO had attracted great interests due to its robust ferroelectric and antiferromagnetic orderings at room temperatures. [2][3][4][5][6][7][8][9][10][11] Under a strong compressive strain ( > 4%), the stable crystal structure of BFO transformed from the rhombohedral-like monoclinics (R) to tetragonal-like monoclinics (T), [ 12 , 13 ] and with suitable strain relaxation through thickness, the coexistence of R-BFO and T-BFO phases can be obtained in the same fi lm. [ 1 , 14-18 ] This mixed-phase system can provide a simulated template to reveal origins of unique physical properties in relaxor and morphotropic phase boundary (MPB) materials, such as the large piezoelectric response and the enhanced ferroelectric polarization. [19][20][21][22] In addition, recent study showed that in the mixedphase BFO, the stripe-shape R-BFO embedded in T-BFO matrix possessed nonzero spontaneous magnetic moments along the long axis of the stripe, [ 23 , 24 ] which opens a new direction for strain-driven physics in ferroic oxides.Creation of T-R phase boundary with controllable ferroic orderings is a critical step towards further mechanism study or novel device realization. It is known that the mixed-phase system can be switched between T-and R-BFO phases by external electric fi elds. [ 25 , 26 ] However, the formation of ordered mixed-phase structure seems diffi cult to be obtained, because it involves the selection between many equivalent pathways during the switching history. This problem is similar to that in creating orderly ferroelastic switching in single-phase ferroelectrics, where several local minimum states possessed compatible electrostatic and elastic energies. [ 27 , 28 ] Balke et al. had demonstrated successful control of ferroelastic switching in single-phase BFO by breaking the spatial symmetry during the domain nucleation. [ 29 ] In mixed-phase BFO, Vasudevan et al. had reported the mechanism of T-R transition and created R-BFO phases with specifi c spatial orientations. [ 30 ] However, each orientation of T-R boundary is satisfi ed with low energy states of two polarization confi gurations, and the control of them is yet not addressed. Moreover, the interactions between ferroic parameters of the created boundary with those of the matrix are still unknown. In this study, we present an elegant method to systematically create T-R mixed-phase stripes with controllable ferroic boundary conditions by a biased atomic force microscope (AFM) tip, and fi nally lead to the aim of electrically controllable magnetism. The key factors and mechanisms to break the equivalent variants during T-R phase nucleation are demonstrated, and the fi ne domain structures at the T-R boundary are also revealed. Besides ferroelectric variants, the ferroelastic orderings of T-R boundaries are controlled by varying the strain-mediated interaction with the T-matrix. I...

Olefin metathesis catalyzed by ruthenium carbenes is a powerful tool for forming organic carbonÀcarbon double bonds, 1 making it useful for the synthetic applications of olefin crossmetathesis, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis polymerization, and ring-closing metathesis. The mechanisms of such catalytic reactions have been explored extensively, and it is widely appreciated that dissociation of an organophosphine ligand is a critical step in forming a 14-electron ruthenacarbene intermediate (denoted as B in Scheme 1) that serves as the active species with trans-olefin coordination to form a ruthenacyclobutane.