Fragile phase stability in (1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 crystals: A comparisons of [001] and [110] field-cooled phase diagrams

Phase diagrams of [001] and [110] field-cooled (FC) (1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 or PMN-xPT crystals have been constructed, based on high-resolution x-ray diffraction data. Comparisons reveal several interesting findings. First, a region of abnormal thermal expansion above the dielectric maximum was found, whose stability range extended to higher temperatures by application of electric field (E). Second, the rhombohedral (R) phase of the ZFC state was replaced by a monoclinic MA in the [001] FC diagram, but with monoclinic MB in the [110] FC. Third, the monoclinic MC phase in ZFC and [001] FC diagram was replaced by an orthorhombic (O) phase in the [110] FC. Finally, in the [001] FC diagram, the phase boundary between tetragonal (T) and MA was extended to lower PT contents (x=0.25); whereas in the [110] FC diagram, this extended region was entirely replaced by the O phase. These results clearly demonstrate that the phase stability of PMN-xPT crystals is quite fragile, depending not only on modest changes in E, but also on the direction along which that E is applied.Comment: 13 pages, 8 figures, 1 tabl

Theoretical study of Si+(2PJ)-RG complexes and transport of Si+(2PJ) in RG (RG = He – Ar)

We calculate accurate interatomic potentials for the interaction of a singly-charged silicon cation with a rare gas atom of helium, neon or argon. We employ the RCCSD(T) method, and basis sets of quadruple- and quintuple- quality; each point is counterpoise corrected and extrapolated to the basis set limit. We consider the lowest electronic state of the silicon atomic cation, Si+(2P), and calculate the interatomic potentials for the terms that arise from this: 2and 2+. We additionally calculate the interatomic potentials for the respective spin-orbit levels, and examine the effect on the spectroscopic parameters; we also derive effective ionic radii for C+ and Si+. Finally, we employ each set of potentials to calculate transport coefficients, and compare these to available data for Si+ in He

Structural studies of Fe0.81Ga0.19 by reciprocal space mapping

Reciprocal lattice mapping has been performed on Fe0.81Ga0.19 crystals by ω–ω/2θ, Ψ–ϕ, and ω–ϕ scans. A strong elongation of the 〈001〉c peak was found along the〈110〉c direction. ω scans revealed short lateral correlation lengths ξ along 〈110〉cand strong diffuse scattering along the 〈001〉c. Multiple domains with monoclinic symmetry (angle ∼190°) were observed by Ψ–ϕ and ω–ϕ scans on the (001)c face, and were also tilted with respect to each other. The results show an average cubic structure with orthorhombic structural modulations, and two structural domain states that result in a limiting monoclinic symmetry

Effects of ac-field amplitude on the dielectric susceptibility of relaxors

The thermally activated flips of the local spontaneous polarization in relaxors were simulated to investigate the effects of the applied-ac-field amplitude on the dielectric susceptibility. It was observed that the susceptibility increases with increasing the amplitude at low temperatures. At high temperatures, the susceptibility experiences a plateau and then drops. The maximum in the temperature dependence of susceptibility shifts to lower temperatures when the amplitude increases. A similarity was found between the effects of the amplitude and frequency on the susceptibility.Comment: 8 pages, 7 figures, Phys. Rev. B (in July 1st

Magnetic Tweed Contrast In Ferromagnetic Shape Memory Alloys

Recently, ferromagnetic martensite, specifically ferromagnetic shape memory alloys (FMSMAs), have received renewed attention because of their large domain motion induced magnetostrictive strains. In the low temperature phase of these alloys, 90◦ magnetic domain walls are simultaneously elastic twin boundaries. Above the temperature at which these alloys undergo a near second order martensitic transformation, their microstructure as observed by two-beam TEM methods, consists of the well known tweed contrast. This structure represents a random mixture of incipient twins of the martensitic phase. The transformation hysteresis of Co-Ni-Ga FMSMAs is quite small. In addition, the alloy is elastically soft similar to others that undergo a near second order martensitic transformation. Therefore, it is possible that magnetic tweed be observed in this alloy. This paper reports on its observation by conventional TEM, electron diffraction and Lorentz microscopy