This work investigates origins of cation ordering in double perovskites using first-principles theory computations combined with machine learning (ML) and causal relations. We have considered various oxidation states of A, A′, B, and B′ from the family of transition metal ions to construct a diverse compositional space. A conventional framework employing traditional ML classification algorithms such as Random Forest (RF) coupled with appropriate features including geometry-driven and key structural modes leads to accurate prediction (∼98%) of A-site cation ordering. We have evaluated the accuracy of ML models by employing analyses of decision paths, assignments of probabilistic confidence bound, and finally a direct non-Gaussian acyclic structural equation model to investigate causality. Our study suggests that structural modes are crucial for classifying layered, columnar, and rock-salt ordering. The charge difference between A and A′ is the most important feature for predicting clear layered ordering, which in turn depends on the B and B′ charge separation. We have also designed mathematical relationships with these features to derive energy differences to form clear layered ordering. The trilinear coupling between tilt, in-phase rotation, and A-site antiferroelectric displacement in the Landau free-energy expansion becomes the necessary condition behind formation of A-site cation ordering.

While bismuth ferrite BiFeO3 (BFO) is a well studied multiferroic material, its electronic and magnetic properties in the presence of A-site dopants have not been explored widely. Here we report the results of a systematic study of the local electronic structure, spontaneous polarization, and magnetic properties of lanthanum (La) and strontium (Sr) doped rhombohedral bismuth ferrite within density functional theory. An enhanced ferroelectric polarization of 122.43 μC/cm2 is predicted in the uniformly doped BiLaFe2O6. We find that substitution of Sr in the A-site drives the system into a metallic state. The nature of magnetism arises mainly from the B-site Fe exhibiting a G-type antiferromagnetic ordering. Our study finds that upon dopant substitution, the local magnetic moment is decreased and its magnitude is dependent on the distance between the Fe and the dopant atom. The correlation between the local moment and the distance between the Fe and the dopant atom is discussed.

No abstract

Abstract.A revised global fit of electroweak ep and νp elastic scattering data has been performed, with the goal of determining the strange quark contribution to the vector and axial-vector form factors of the nucleon in the momentum-transfer range 0 < Q 2 < 1 GeV 2 . The two vector (electric and magnetic) form factors G s E (Q 2 ) and G s M (Q 2 ) are strongly constrained by ep elastic scattering data, while the major source of information on the axial-vector form factor G s A (Q 2 ) is νp scattering data. Combining the two kinds of data into a single global fit makes possible additional precision in the determination of these form factors, and provides a unique way to determine the strange quark contribution to the nucleon spin, ∆S , independently of leptonic deep-inelastic scattering. The fit makes use of data from the BNL-E734, SAMPLE, HAPPEx, G0, and PVA4 experiments; we will also compare the result of the fit with recent data from MiniBooNE, and anticipate how this fit can be improved when new data from MicroBooNE become available. OverviewThe strange quark contribution to the elastic form factors of the nucleon has been the subject of intense experimental scrutiny for several decades. Experiments involving elastic scattering of neutrinos and anti-neutrinos (BNL E734 [1]), and electrons (SAMPLE [2], HAPPEx [3][4][5][6][7], G0 [8,9], and PVA4 [10][11][12]) from nucleons and nuclei have explored the strange quark presence in the nucleon by exploiting the electromagnetic and weak interactions in a variety of ways. These special data permit a simultaneous determination [13] of the strange quark contribution to the electric (G s E (Q 2 )), magnetic (G s M (Q 2 )), and axial (G s A (Q 2 )) form factors of the nucleon, which respectively allow us to understand how the strange quark contributes to the distribution of charge, current, and spin inside the nucleon. A global fit of these data has been performed, which sets strong limits on the size and Q 2 -dependence of G s E (Q 2 ) and G s M (Q 2 ), and points out the need for additional neutrino scattering data at low Q 2 to complete a measurement of G s A (Q 2 ). Strangeness Form FactorsSince the strange and anti-strange quarks have opposite electric charges, then they contribute to the strangeness electric form factor G s E with opposite sign; therefore, if the s ands distributions in the a