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Epitaxial (001)-, (118)-, and (104)-oriented Nd-doped Bi 4 Ti 3 O 12 films have been grown by pulsed-laser deposition from a Bi 4-x Nd x Ti 3 O 12 (x=0.85) target on SrRuO 3 coated single-crystal (100)-, (110)-, and (111)-oriented SrTiO 3 substrates, respectively. X-ray diffraction illustrated a unique epitaxial relationship between film and substrate for all orientations. We observed a strong dependence of ferroelectric properties on the film orientation, with no ferroelectric activity in an (001)-oriented film; a remanent polarization, 2P r , of 12 µC/cm 2 and coercive field, E c , of 120 kV/cm in a (118)-oriented film; and 2P r = 40 µC/cm 2 , E c = 50 kV/cm in a (104)-oriented film. The lack of ferroelectric activity along the c-axis is consistent with the orthorhombic nature of the crystal structure of the bulk material, as determined by powder neutron diffraction.

Temperature dependent X-ray diffraction and Raman spectroscopic studies were carried out on the flux grown single crystals of gallium ferrite with Ga:Fe ratio of 0.9:1

The dehydratase (DH) domain of module 4 of the 6-deoxyerythronolide B synthase (DEBS) has been shown to catalyze an exclusive syn elimination/syn addition of water. Incubation of recombinant DH4 with chemoenzymatically prepared anti-(2R,3R)-2-methyl-3-hydroxypentanoyl-ACP (2a-ACP) gave the dehydration product 3-ACP. Similarly, incubation of DH4 with synthetic 3-ACP resulted in the reverse enzyme-catalyzed hydration reaction, giving a ~3:1 equilbrium mixture of 2a-ACP and 3-ACP. Incubation of a mixture of propionyl-SNAC (4), methylmalonylCoA, and NADPH with the DEBS β-ketoacyl synthase -acyl transferase [KS6][AT6] didomain, DEBS ACP6, and the ketoreductase domain from tylactone synthase module 1 (TYLS KR1) generated in situ anti-2a-ACP that underwent DH4-catalyzed syn dehydration to give 3-ACP. DH4 did not dehydrate either syn-(2S,3R)-2b-ACP, syn-(2R,3S)-2c-ACP, or anti-(2S,3S)-2d-ACPgenerated in situ by DEBS KR1, DEBS KR6, or the rifamycin synthase KR7 (RIFS KR7), respectively. Similarly, incubation of a mixture of (2S,3R)-2-methyl-3-hydroxypentanoyl-Nacetylcysteamine thioester (2b-SNAC), and NADPH with DEBS [KS6] [AT6], DEBS ACP6, and TYLS KR1 gave anti-(2R,3R)-6-ACP that underwent syn dehydration catalyzed by DEBS DH4 to give (4R,5R)-(E)-2,4-dimethyl-5-hydroxy-hept-2-enoyl-ACP (7-ACP). The structure and stereochemistry of 7 were established by GC-MS and LC-MS comparison of the derived methyl ester 7-Me to a synthetic sample of 7-Me.Of the more than 2000 non-aromatic polyketides, the vast majority contain one or more disubstituted or trisubstituted double bonds, most of which have E (trans) geometry.1 Moreover, essentially all polyketides that do not themselves display a double bond are biosynthesized by way of one or more unsaturated polyketide chain elongation intermediates. Thus although 6-deoxyerythronolide B (1, 6-dEB), the parent aglycone of the erythromycin family of antibiotics, does not have any double bonds in the final Direct evidence for the intermediacy of an unsaturated polyketide in erythromycin biosynthesis first came from disruption of the NADPH-binding motif of the ER4 domain, resulting in accumulation of a derivative of the corresponding (E)-Δ 6,7 -anhydro-6-dEB by mutants of the erythromycin producer Saccharopolyspora erythraea.4 Although the stereochemistry of the substrate for the DEBS DH4 dehydratase is not known, the responsible ketoreductase, DEBS KR4, is predicted to generate the (3R)-diastereomer of the 2-methyl-3-hydroxyacyl-ACP pentaketide, as deduced from the presence of a Leu-Ala-Asp triad closely correlated with the formation of (3R)-3-hydroxyacyl-ACP polyketide intermediates.5 Indeed, the vast majority of KR domains that are paired with a DH domain appear to harbor a conserved "Leu-Asp-Asp" motif.5a,b DEBS KR4 is also predicted to belong to the class of non-epimerizing ketoreductases, which would give rise to a (2R)-methyl group in the reduced product.5cTo establish the substrate specificity and stereochemical course of the DEBS DH4-catalyzed dehydration we used a che...

We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric

We show the effect of composition on structural and magnetic characteristics of pure phase polycrystalline Ga 2-x Fe x O 3 (GFO) for compositions between 0.8 ≤ x ≤ 1.3. X-ray analysis reveals that lattice parameters of GFO exhibit a linear dependence on Fe content in single phase region indicating manifestation of Vegard's law. Increasing Fe content of the samples also leads to stretching of bonds as indicated by the Raman peak shifts. Further, low temperature magnetic measurements show that the coercivity of the samples is maximum for Ga:Fe ratio of 1:1 driven by a competition between decreasing crystallite size and increasing magnetic anisotropy.

In this paper, we report on the effect of Sm doping on the phase evolution and properties of phase-pure Bi1−xSmxFeO3 (BSFO) ceramics synthesized via a conventional solid-state-reaction method. We find that upon calcination, Sm doping of bismuth ferrite promotes the formation of perovskitic phase and leads to the elimination of the secondary phases. On the other hand, undoped compositions do not yield completely phase-pure samples and contain secondary phases such as Bi25FeO40. Differential thermal analysis corroborates the sequence of phase evolution as examined from the x-ray diffraction patterns. A thermodynamic analysis, based on the bond energy, has been carried out to explain the effect of doping on the stabilization of perovskite structured phase upon Sm doping and is well supported by the thermal analysis results. Vibrating sample magnetometry measurements show that BSFO samples possess higher room temperature remnant magnetization than the undoped samples. Temperature dependent magnetic measurements suggest an antiferromagnetic behavior in the BSFO samples with a Néel temperature of ∼370°C, absent in the undoped samples. Mössbauer spectroscopy on Sm-doped specimens reveals the presence of phase-pure BSFO with absence of any Fe+2 ions. Interestingly, doped samples exhibit an order of magnitude increase in the leakage current density.

We present a theoretical study of the structure-property correlation in gallium ferrite, based on first-principles calculations followed by a subsequent comparison with experiments. The local spin density approximation (LSDA + U ) of the density functional theory has been used to calculate the ground state structure, electronic band structure, density of states and Born effective charges. The calculations reveal that the ground state structure is orthorhombic Pc2 1 n having A-type antiferromagnetic spin configuration, with lattice parameters matching well with those obtained experimentally. Plots of the partial density of states of constituent ions exhibit noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density and electron localization function show a largely ionic character of the Ga/Fe-O bonds which is also supported by a lack of any significant anomaly in the calculated Born effective charges with respect to the corresponding nominal ionic charges. The calculations show a spontaneous polarization of ∼59 μC cm −2 along the b-axis which is largely due to asymmetrically placed Ga1, Fe1, O1, O2 and O6 ions.