Browsing by Author "Devreugd, Christopher P."
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- Lead-free and lead-based ABO(3) perovskite relaxors with mixed-valence A-site and B-site disorder: comparative neutron scattering structural study of (Na1/2Bi1/2) TiO3 and Pb(Mg1/3Nb2/3)O-3Ge, Wenwei; Devreugd, Christopher P.; Phelan, Daniel; Zhang, Qinhui; Ahart, Muhtar; Li, Jiefang; Luo, Haosu; Boatner, Lynn A.; Viehland, Dwight D.; Gehring, Peter M. (American Physical Society, 2013-11-01)We report the results of neutron elastic-scattering measurements made between -250 degrees C and 620 degrees C on the lead-free relaxor (Na1/2Bi1/2)TiO3 (NBT). Strong, anisotropic, elastic diffuse scattering intensity decorates the (100), (110), (111), (200), (210), and (220) Bragg peaks at room temperature. The wave-vector dependence of this diffuse scattering is compared to that in the lead-based relaxor Pb(Mg1/3Nb2/3)O-3 (PMN) to determine if any features might be common to relaxors. Prominent ridges in the elastic diffuse scattering intensity contours that extend along < 110 > are seen that exhibit the same zone dependence as those observed in PMN and other lead-based relaxors. These ridges disappear gradually on heating above the cubic-to-tetragonal phase transition temperature T-CT = 523 degrees C, which is also near the temperature at which the dielectric permittivity begins to deviate from Curie-Weiss behavior. We thus identify the < 110 >-oriented ridges as a relaxor-specific property. The diffuse scattering contours also display narrower ridges oriented along < 100 > that are consistent with the x-ray results of Kreisel et al. [Phys. Rev. B 68, 014113 (2003)]; these vanish near 320 degrees C, indicating that they have a different physical origin. The < 100 >-oriented ridges are not observed in PMN. We observe no equivalent relaxor-specific elastic diffuse scattering from the homovalent relaxor analogues K0.95Li0.05TiO3 (A-site disordered) and KTa0.95Nb0.05O3 (B-site disordered). This suggests that the < 110 >-oriented diffuse scattering ridges are correlated with the presence of strong random electric fields and invites a reassessment of what defines the relaxor phase. We find that doping NBT with 5.6% BaTiO3, a composition close to the morphotropic phase boundary with enhanced piezoelectric properties, increases the room-temperature correlation length along [1 (1) over bar0] from 40 to 60 angstrom while doubling the associated integrated diffuse scattering. Similar behavior was reported by Matsuura et al. [Phys. Rev. B 74, 144107 (2006)] for morphotropic compositions of PMN doped with PbTiO3. Finally, we comment on the recent observation of monoclinicity in NBT at room temperature by placing a strict bound on the strength of the (1/2 1/2 1/2) superlattice reflection associated with the Cc space group based on the atomic coordinates published in the x-ray study by Aksel et al. [Appl. Phys. Lett. 98, 152901 (2011)] for NBT. We show that a skin effect, analogous to that reported in the relaxors PZN-xPT and PMN-xPT, can reconcile our neutron single-crystal data with the x-ray powder data of Aksel et al. [Appl. Phys. Lett. 98, 152901 (2011)]. Our finding of a skin effect in a lead-free, A-site disordered, heterovalent relaxor supports the idea that it arises in the presence of strong random electric fields.
- Monoclinic M-C phase in (001) field cooled BaTiO3 single crystalsCao, Hu; Devreugd, Christopher P.; Ge, Wenwei; Li, Jiefang; Viehland, Dwight D.; Luo, Haosu; Zhao, X. Y. (AIP Publishing, 2009-01-01)We report here the finding of a new phase in BaTiO3 single crystals. High precision x-ray diffraction investigations of (001) field cooled crystals have shown the presence of a monoclinic M-C phase for temperatures below 300 K. This M-C phase is shown to be stable upon removal of the electric field. The results demonstrate the presence of structurally bridging low symmetry phases that lie between tetragonal and rhombohedral ones in this classic perovskite system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.
- A monoclinic-tetragonal ferroelectric phase transition in lead-free (K0.5Na0.5)NbO3-xLiNbO3 solid solutionGe, Wenwei; Ren, Yang; Zhang, Jialiang; Devreugd, Christopher P.; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-05-15)A monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na0.5)NbO3-5%LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements. At ambient temperature, the lattice parameters of this monoclinic structure were (a(m), b(m), c(m); beta) = (4.015 angstrom, 3.944 angstrom, 3.987 angstrom; 90.34 degrees). This monoclinic phase transformed to a tetragonal (P4mm) one on heating between 340 K and 360K. The results demonstrate the presence of structurally bridging low symmetry monoclinic phase in (K0.5Na0.5)NbO3-x%LiNbO3 solid solution system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4716027]
- Role of Nanoscale Precipitates on the Enhanced Magnetostriction of Heat-Treated Galfenol (Fe1-xGax) AlloysCao, Hu; Gehring, Peter M.; Devreugd, Christopher P.; Rodriguez-Rivera, J. A.; Li, J.; Viehland, Dwight D. (American Physical Society, 2009-03-27)We report neutron diffuse scattering measurements on highly magnetostrictive Fe1-xGax alloys (0.14 < x < 0.20) with different thermal treatments. This diffuse scattering scales with magnetostriction and exhibits asymmetric peaks at the (100) and (300) reciprocal lattice positions that are consistent with the coexistence of short-range ordered, coherent nanometer-scale precipitates embedded in a long-range ordered, body-centered cubic matrix. A large peak splitting is observed at (300) for x=0.19, which indicates that the nanoprecipitates are not cubic and have a large elastic strain. This implies a structural origin for the enhanced magnetostriction.
- Ultrahigh electromechanical response in (1-x)(Na0.5Bi0.5)TiO3-xBaTiO(3) single-crystals via polarization extensionGe, Wenwei; Luo, Chengtao; Zhang, Qinhui; Devreugd, Christopher P.; Ren, Yang; Li, Jiefang; Luo, Haosu; Viehland, Dwight D. (American Institute of Physics, 2012-05-01)The dielectric, ferroelectric, and electric field-induced strain response of [001]-and [101]-oriented 0.944Na(0.5)Bi(0.5)TiO(3)-0.056BaTiO(3) (0.944NBT-0.056BT) single crystals were investigated as a function of temperature and dc bias (E). An ultrahigh electromechanical response with large amplitude longitudinal piezoelectric coefficients as high as d(33)=2500 pm/V was found in [001](PC) oriented 0.944NBT-0.056BT single crystals near a depolarization temperature of T-d = 130 degrees C. In-situ XRD revealed that the enhanced piezoelectric properties resulted from a polarization extension between a polar pseudocubic phase with a slight tetragonal (P4bm) distortion and a polar tetragonal one with a large tetragonal distortion of c/a = 1.02. Our findings indicate a potential approach to high performance lead-free piezoelectrics, via polarization extension. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709619]
- X-ray diffraction study of the pressure-induced bcc-to-hcp phase transition in the highly magnetostrictive Fe0.81Ga0.19 alloyAhart, Muhtar; Devreugd, Christopher P.; Li, Jiefang; Viehland, Dwight D.; Gehring, Peter M.; Hemley, Russell J. (American Physical Society, 2013-11-07)High-pressure x-ray diffraction measurements were performed at room temperature on single crystals of the highly magnetostrictive alloy Fe0.81Ga0.19 (galfenol). This alloy has a bcc crystal structure at ambient pressure but undergoes a bcc-to-hcp phase transition at 24 GPa on compression. A large hysteresis loop is observed in which the reversed transition occurs at 13 GPa on decompression. The midpoint of this transition is 18.5 GPa. The measured bulk modulus of this material is 182 (+/- 17) GPa, which is comparable to that of pure iron. As with iron, the hcp structure of the alloy can be derived from a compression of the bcc lattice along [001] that is accompanied by shearing along [1 (1) over bar0]. Our results indicate that the addition of Ga shifts the bcc-to-hcp transition from 13 GPa in pure iron to 18.5 GPa, and we speculate that this is due to the larger atomic radius of Ga. A uniaxial loading of 3 GPa completely suppresses the diffuse scattering in Fe0.81Ga0.19. We ascertain that the magnetostrictive properties of the alloy are reduced under pressure.