Browsing by Author "Studer, AJ"

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    Anomalous precursive behaviour for the martensitic material Ni 0.625 Al 0.375
    (Australian Institute of Physics, 2011-02-02) Finlayson, TR; Danilkin, SA; Studer, AJ; Whitfield, RE
    NixAl1-x alloys for 0.615 < x < 0.64 undergo a martensitic transformation upon cooling from a CsCl-type structure to a pseudo-orthorhombic structure [1]. The transformation temperature is extremely composition dependent [2] and for Ni0.625Al0.375 is ~ 80 K [1]. In previous research using an approximate cube of single crystal having x = 0.625 [3], significant strain anisotropy was detected above 80 K. It was suggested that this anomalous strain anisotropy indicated the presence of a martensite precursor within the cubic “parent” phase. The aim of the current research project is to investigate the precursive structural behaviour in the above Ni0.625Al0.375 single crystal using both elastic and inelastic neutron scattering. Results from initial experiments at both the Wombat and Taipan instruments at the Opal Research Reactor will be presented and discussed in relation to previously published strain anisotropy data determined using variable temperature, capacitance dilatometry [3].
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    Apparent critical phenomena in the superionic phase transition of Cu2-xSe
    (IOP Science, 2016-01-11) Kang, SD; Danilkin, SA; Aydemir, U; Avdeev, M; Studer, AJ; Snyder, GJ
    The superionic phase transition of Cu2-xSe accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. Understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
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    Austenite formation kinetics from multicomponent cementite-ferrite aggregates by in situ neutron powder diffraction
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Wu, Y; Wang, L; Sun, W; Styles, MJ; Studer, AJ; Brechet, Y; Hutchinson, C
    The development of third generation advanced high strength steels (AHSS) as the next generation sheet steel grade is driven by the automotive industry. The key processing step is called ‘intercritical annealing’ at temperatures in the region of the ferrite and austenite two-phase field. The transformed austenite during intercritical annealing will be retained at a metastable state in the final microstructure. Controlling the fraction and chemistry of austenite and resulting mechanical properties is critical for many AHSS. The kinetics of austenite formation depend sensitively on the initial microstructure and annealing conditions. In this talk, we will present detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of AHSS grades via in situ neutron powder diffraction at WOMBAT. The quantitative phase analyses highlight that the saturation of transformation kinetics in relation to global equilibrium is affected by the competition between different interface migration. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics. The experimental and computational work in this contribution would guide future processing and alloy design of AHSS.
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    Charge-order melting in charge-disproportionated perovskite CeCu3Fe4O12
    (Americal Chemical Society, 2014-10-21) Yamada, I; Etani, H; Hayashi, N; Mizumaki, M; Ueda, S; Abe, H; Liss, KD; Studer, AJ; Ozaki, T; Mori, S; Takahashi, R; Irifune, T
    A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge-ordering. © 2014, American Chemical Society.
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    Chemical pressure effects on crystal and magnetic structures of bilayer manganites PrA2Mn2O7 (A = Sr or Ca)
    (AIP Publishing, 2016-06-03) Deng, G; Sheptyakov, D; Pomjakushin, V; Medarde, M; Pomjakushina, E; Conder, K; Kenzelmann, M; Studer, AJ; Gardner, JS; McIntyre, GJ
    The crystal and magnetic structures of the bilayer manganites PrSr2Mn2O7 (PSMO) and PrCa2Mn2O7 (PCMO) have been studied by neutron powder diffraction. It was found that PSMO crystallizes in space group I4/mmm, while PCMO adopts space group Cmc21 at room temperature. The difference in the structure arises from chemical pressure induced by the Ca substitution for Sr on the A sites, which causes different Jahn-Teller distortions. In PSMO, the MnO6 octahedra suffer a small elongated distortion, while those in PCMO adopt strong compressed distortion along the axial direction. In addition, the octahedra in PCMO show a+b0c0 rotation and a0b+c+ tilting in the Glazer notation in comparison to PSMO. As a result, these two compounds adopt very different magnetic structures: The magnetic structure of PSMO is an A-type magnetic structure (Im'm'm) with propagation vector k = (0, 0, 1) and magnetic moments in the ab plane. In contrast, a C-type antiferromagnetic magnetic structure (Cm'c2′1) with the multiple propagation vectors (k = (0, 12, 12) and (0, 12, 0)) and magnetic moments mainly along the b axis is found in PCMO. The critical exponent of the magnetic phase transition is around 0.345 for PSMO and 0.235 for PCMO, indicating 3D and 2D XY transitions, respectively. The strong Jahn-Teller distortion induced by the chemical pressure is believed to suppress the double exchange and favour super-exchange in PCMO, leading to the dramatic difference in the magnetic structure. © 2016 Author(s). Published by AIP Publishing.
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    Coexistence of long-range magnetic ordering and singlet ground state in the spin-ladder superconductor SrCa13Cu24O41
    (American Physical Society, 2013-11-26) Deng, GC; Kenzelmann, M; Danilkin, SA; Studer, AJ; Pomjakushin, V; Imperia, P; Pomjakushina, E; Conder, K
    A long-range magnetic order was discovered in the quasi-one-dimensional spin-ladder compound SrCa13Cu24O41 by susceptibility, specific heat, and neutron diffraction experiments. The temperature dependence of the magnetic Bragg peak intensity could be well fitted to the power law with a transition temperature TN = 4.23 K and a critical exponent β = 0.28, indicating a three-dimensional phase transition for a low-dimensional magnet. A computer program was coded and found two possible magnetic structure models fitting best with all the observed magnetic peaks. These models suggest the spin-ladder sublattice is magnetically ordered with Cu moments aligning along the a axis. The spin interactions are primarily antiferromagnetic along rungs and legs, while there are ferromagnetic clusters along legs. Surprisingly, the singlet-triplet spin-gap excitation is observable above and below TN, indicating a coexistence of the spin-singlet ground state and long-range magnetic ordering state in this compound. © 2013 American Physical Society.
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    Combined experimental and computational study of oxide ion conduction dynamics in Sr2Fe2O5 brownmillerite
    (American Chemical Society, 2013-08-13) Auckett, JE; Studer, AJ; Pellegrini, E; Ollivier, J; Johnson, MR; Schober, H; Miiller, W; Ling, CD
    We report a detailed study of the dynamics of oxide ionic conduction in brownmillerite-type Sr2Fe2O5, including lattice anisotropy, based on neutron scattering studies of a large (partially twinned) single crystal in combination with ab initio molecular dynamics simulations. Single-crystal diffraction reveals supercell peaks due to long-range ordering among chains of corner-sharing FeO4 tetrahedra, which disappears on heating above 540 °C due to confined local rotations of tetrahedra. Our simulations show that these rotations are essentially isotropic, but are a precondition for the anisotropic motion that moves oxide ions into the tetrahedral layers from the octahedral layers, which we observe experimentally as a Lorentzian broadening of the quasielastic neutron scattering spectrum. This continual but incoherent movement of oxide ions in turn creates conduction pathways and activates long-range diffusion at the interface between layers, which appears to be largely isotropic in two dimensions, in contrast with previously proposed mechanisms that suggest diffusion occurs preferentially along the c axis.© 2013, American Chemical Society.
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    A comparative study of magnetic behaviors in TbNi2, TbMn2 and TbNi2Mn
    (AIP Publishing LLC., 2014-01-01) Wang, JL; Din, MFM; Kennedy, SJ; Hong, F; Campbell, SJ; Studer, AJ; Wu, GH; Cheng, ZX; Dou, SX
    All TbNi2, TbMn2, and TbNi2Mn compounds exhibit the cubic Laves phase with AB2-type structure in spite of the fact that the ratio of the Tb to transition-metal components in TbNi2Mn is 1:3. Rietveld refinement indicates that in TbNi2Mn the Mn atoms are distributed on both the A (8a) and B (16d) sites. The values of the lattice constants were measured to be a¼14.348A ° (space group F-43 m), 7.618A ° , and 7.158A ° (space group Fd-3 m) for TbNi2, TbMn2, and TbNi2Mn, respectively. The magnetic transition temperatures TC were found to be TC¼38K and TC¼148K for TbNi2 and TbNi2Mn, respectively, while two magnetic phase transitions are detected for TbMn2 at T1¼20K and T2¼49 K. Clear magnetic history effects in a low magnetic field are observed in TbMn2 and TbNi2Mn. The magnetic entropy changes have been obtained. © 2014 AIP Publishing LLC.
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    Comparison of thermal stability in MAX 211 and 312 phases
    (Insitute of Physics, 2010-05-03) Pang, WK; Low, IM; O'Connor, BH; Studer, AJ; Peterson, VK; Sun, ZM; Palmquist, JP
    The susceptibility of four MAX phases (Ti 2 AlC, Cr 2 AlC, Ti 3 AlC 2 , and Ti 3 SiC 2 ) to high-temperature thermal dissociation in vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of M and A elements, forming a surface coating of MC. The apparent activation energies for the decomposition of sintered Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC were determined to be 179.3, -71.9, and 85.7 kJ mol −1 , respectively. The spontaneous release of Ti 2 AlC and TiC from de-intercalation during decomposition of Ti 3 AlC 2 resulted in a negative activation energy.© 2010, Insitute of Physics
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    A correlated electron diffraction, in situ neutron diffraction and dielectric properties investigation of poled (1-x)Bi0.5Na0.5TiO3-xBaTiO3 ceramics
    (American Institute of Physics, 2011-10-15) Wang, J; Liu, Y; Withers, RL; Studer, AJ; Li, Q; Norén, L; Guo, YP
    A correlated electron diffraction, temperature-dependent in situ neutron diffraction, and temperature-dependent dielectric properties investigation of poled (1-x)Bi(0.5)Na(0.5)TiO(3)-xBaTiO(3) (BNTBT100x) (x = 0.04, 0.07, and 0.12) samples has been carried out. The results show that the depolarization temperature, T(d), of the rhombohedral BNTBT 4 sample is associated with the disappearance of G +/- 1/2 [111]*(p) satellite reflections and a(-)a(-)a(-) octahedral tilting while that of the BNTBT 12 sample is associated with a metrically tetragonal to metrically cubic or pseudo-cubic symmetry. In the case of the poled BNTBT 7 sample in the MPB region, the dielectric properties show a quite distinct two stage transition from a room temperature clearly metrically tetragonal phase again to a metrically cubic or pseudo-cubic symmetry above 150 degrees C. There is no apparent change in its average structure in vicinity of T(d) in BNTBT 7. Electron diffraction shows the presence of considerable octahedral tilt twin disorder in all three samples. (C) 2011 American Institute of Physics.
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    Critical role of the coupling between the octahedral rotation and a-site ionic displacements in PbZrO3-based antiferroelectric materials investigated by in situ neutron diffraction
    (American Physical Society, 2017-12-21) Lu, T; Studer, AJ; Yu, DH; Withers, RL; Feng, Y; Chen, H; Islam, SS; Xu, Z; Liu, Y
    This in situ neutron-diffraction study on antiferroelectric (AFE) Pb0.99(Nb0.02Zr0.65Sn0.28Ti0.05)O3 polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and A-site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and E-field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and A-site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples’ FE and AFE properties. ©2017 American Physical Society - Open access
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    Crystal and magnetic structures in perovskite-related La1-xCaxFeO3-δ (x=0.2, 0.33)
    (Elsevier, 2011-12) Hudspeth, JM; Stewart, GA; Studer, AJ; Goossens, DJ
    Using sol gel synthesis, single phase perovskite-related compounds in the family La1-xCaxFeO3-δ have been formed for x=0.2 and x=0.33, but not for x=0.5. The x=0.2 and x=0.33 compounds are isostructural with LaFeO3 (Pnma). The magnetic structure of La 0.8 Ca0.2FeO3-δ has been studied through Mössbauer spectroscopy and neutron powder diffraction. La 0.8 Ca 0.2FeO3-δ is a G-type antiferromagnet with a magnetic moment magnitude of 3.0±0.2μB at room temperature. The reduction in the magnitude of the antiferromagnetic moment compared to that published for LaFeO3 is explained by the measurement being taken at room temperature rather than 4 K and by the presence of Fe4 ions which have weaker exchange interactions than Fe3, causing a strong reduction in TN. Room temperature Mössbauer shows a broad magnetic hyperfine field distribution on the Fe sites in both La0.8 Ca0.2FeO3-δ and La0.67 Ca 0.33FeO3-δ. On cooling, disproportionation of Fe14 into Fe3 and Fe5 is apparent, and the resulting Fe5 sextet measured at low temperature gives a reliable measure of the Fe4 fraction. This in turn shows that creation of high-oxidation-state Fe is the dominant charge balance mechanism on doping Ca2 into the Ln3 site indicating a disordered distribution of Fe3 and Fe4. The lack of broadening of the Fe 5 sextet suggests that there may be ordering in the distribution of Fe5. © 2011 Elsevier Ltd.
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    The crystal and magnetic structures of LaCa2Fe3O8 and NdCa2Fe3O8
    (Institute of Physics, 2009-03-25) Hudspeth, JM; Goossens, DJ; Studer, AJ; Withers, RL; Norén, L
    The crystal and magnetic structures of LaCa2Fe3O8 and NdCa2Fe3O8 have been established using a combination of x-ray, neutron and electron diffraction. It was already considered likely that LaCa2Fe3O8 and NdCa2Fe3O8 were made up of stacked perovskite-like layers of FeO6 octahedra, with every third layer being replaced by a layer of tetrahedrally coordinated Fe, rather like a variation on the Brownmillerite (Ca2Fe2O5) structure type. We have gone further and determined a likely space group for this Grenier phase and determined the magnetic structure of the compounds at room temperature. The space group is found to be P2(1)ma (b axis as the long axis), and the crystal structure has been refined, subject to the stacking faulting along the long axis that is apparent in electron diffraction patterns. The magnetic structure of LaCa2Fe3O8 is shown to consist of antiferromagnetically ordered Fe3+ ions on a collinear G-type antiferromagnetic structure, with the magnetic moments most likely (anti) parallel with the c axis, and of magnitude 3.4 +/- 0.2 mu(B) (3.6 +/- 0.2 mu(B) for NdCa2Fe3O8). The result is reasonable given the magnetic structures of the end members of the La1-xCaxFeO3 series, LaFeO3 (x = 0) and Ca2Fe2O5 (x = 1). © 2009, Institute of Physics
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    Determining fundamental properties from diffraction: electric field induced strain and piezoelectric coefficient
    (Australian Institute of Physics, 2016-02-04) Hinterstein, M; Studer, AJ; Hoffman, M
    Piezoelectric ceramics exhibit the remarkable property to couple elastic strain and polarization under the influence of an applied electric field. Among the various types of piezoelectric devices, especially actuators rely on high electric fields to generate high strains and forces. Prominent examples for actuators are multilayer stack actuators used for nanopositioning or in modern combustion engines for automobiles to control injection cycles. The two most important characteristics of this class of materials are macroscopic strain and piezoelectric coefficient. Despite extensive studies and elaborated measurement techniques, the correlation between macroscopic strain and structural response is still not fully understood. Most of the relevant systems found up to now are compositions close to phase boundaries linking highly correlated phases. This results in major challenges for structural analyses due to overlapping reflections. Apart from the well-known field induced structural responses such as domain switching and the converse piezoelectric effect we recently identified field induced phase transitions in different systems as an additional poling mechanism. In order to resolve all three involved poling mechanisms within only one experiment we developed a structural analysis technique with in situ X-ray and neutron powder diffraction data. The results not only separately reveal the contributions of each poling mechanism to the macroscopic strain, but also different behaviours of the individual phases. The calculation of the elastic strain perfectly matches the macroscopic observations, confirming the accuracy of the applied models. Since this method yields fundamental information such as the crystal structure as a function of applied electric field, we were able to calculate the piezoelectric coefficient for the individual phases based on information on the atomic scale. In this contribution we present the latest research on the elucidation of strain mechanisms and fundamental properties in piezoceramics.
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    Development of a new instrument to observe time-resolved neutron diffraction intensities in association with phase transitions
    (Australian Institute of Physics, 2005-01-31) Daniels, JE; Studer, AJ; Finlayson, TR; Hagen, ME
    The study of time-resolved diffraction intensities during a phase transition is important for gaining an understanding of the kinetics involved. Unfortunately the flux needed in order to achieve good counting statistics for a diffraction experiment during a single phase transition is very high. This problem is then compounded if the time scales which need to be observed are very small. Therefore techniques which can take advantage of the reversibility of some phase transitions are potentially beneficial in order to build up statistics. Stroboscopic techniques have been used in recent times to observe diffraction peak intensities with very good time resolution during the application of some type of perturbing field, driving a transition. Most commonly, and as will be the case with this instrument, high electric fields are used to switch single-crystal samples between their paraelectric and ferroelectric phases. Diffraction peaks are observed as a function of time during the switching period [1]. Other types of cycles which have also been used are stress [2], and temperature [3]. In order to carry out these types of experiments, a new capability has been added to The Australian Stress Scanner (TASS) instrument [4] at the High Flux Australian Reactor (HIFAR) operated by the Australian Nuclear Science and Technology Organisation (ANSTO). TASS is the former Triple Axis Spectrometer which, within the last couple of years, has been significantly refurbished (including the introduction of a multi-line, position-sensitive detector) to function as a two-axis diffractometer for strain mapping in engineering materials. This capability will allow for such stroboscopic experiments to be performed using the switching of high-voltage electric fields. The exact operation of the device is outlined in the experimental details section below. The common ferroelectric material, triglycine sulphate, will be used as a model crystal for the commissioning of the stroboscopic technique at HIFAR since, in a previous study involving stroboscopic diffraction intensity measurements at the ISIS [5], most unusual time dependencies for diffraction peak intensities from a TGS crystal in response to the switching of high-voltage electric fields applied to the crystal were observed.
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    Diffraction study on the thermal stability of Ti3SiC2/TiC/TiSi2 composites in vacuum
    (American Institute of Physics, 2009-06-29) Pang, WK; Low, IM; O’Connor, BH; Studer, AJ; Peterson, VK; Palmquist, JP
    Titanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this paper, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites at up to 1550° C was studied using in‐situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400–1450°C to form Ti3SiC2. Above 1400° C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formation and decomposition of Ti3SiC2 was determined. © 2009 American Institute of Physics
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    Diffuse scattering and QENS study of copper chalcogenides
    (Australian Institute of Physics, 2009-02-05) Danilkin, SA; Avdeev, M; Studer, AJ; Ling, CD; Macquart, RB; Russina, M; Izaola, Z
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    Domain fragmentation during cyclic fatigue in 94%Bi(1/2)Na(1/2)TiO3-6%BaTiO3.
    (American Institute of Physics, 2012-01-01) Simons, H; Glaum, J; Daniels, JE; Studer, AJ; Liess, A; Rodel, J; Hoffman, M
    The fatigue of the lead-free piezoceramic 94%(Bi1/2Na1/2)TiO3-6%BaTiO3 was investigated under bipolar electric fields. Degradation of the polarization, strain, and permittivity was measured during the fatigue process, and correlated with structural data measured at incremental points in the fatigue process using neutron diffraction. The results suggest a two-stage fatigue mechanism whereby, following a field-induced phase transformation to a poled ferroelectric state, the domain structure becomes progressively fragmented by a repetitive process of domain wall pinning and subdivision. © 2012, American Institute of Physics.
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    Domain wall and interphase boundary motion in a two-phase morphotropic phase boundary ferroelectric: Frequency dispersion and contribution to piezoelectric and dielectric properties
    (American Physical Society, 2012-07-12) Jones, JL; Aksel, E; Tutuncu, G; Usher, TM; Chen, J; Xing, XR; Studer, AJ
    In ferroelectric materials, enhanced dielectric and piezoelectric property coefficients are found in compositions near morphotropic phase boundaries (MPBs). The material response in these compositions may be contributed by enhanced intrinsic piezoelectric distortions or increased interface motion, e.g., contributions from domain wall and interphase boundary motion, though the relative effect of these mechanisms in different materials is not yet well understood. One of the major challenges to developing this understanding is the availability and sensitivity of in situ characterization techniques, particularly during the application of cyclic electric fields of subcoercive or weak amplitude, conditions at which the property coefficients are measured. Here, we use time-resolved neutron diffraction to resolve the subtle electric-field-induced crystallographic strain mechanisms in a prototypical MPB composition, 36%BiScO(3)-64%PbTiO(3), that contains coexisting monoclinic and tetragonal phases. We observe multiple cooperative electromechanical effects including domain wall motion in both the monoclinic and tetragonal phases, interphase boundary motion between the two phases, and electric-field-induced lattice strains. The measured effects span four orders of magnitude in frequency, facilitating the discrimination of intrinsic and extrinsic contributions to properties. Domain wall motion in the monoclinic phase dominates the response, leading to shifts of diffraction peaks as high as 2300 pm/V; these shifts reflect the field-induced changes in average pseudocubic (00h) lattice spacing of the monoclinic phase parallel to the electric field. Domain wall motion in the tetragonal phase is also readily apparent and exhibits a degree of frequency dispersion similar to that measured in both the relative permittivity and piezoelectric coefficients at similar conditions. © 2012, American Physical Society.
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    Doping-driven structural phase transition and loss of superconductivity in MxFe1−xSeδ (M=Mn, Cu)
    (American Physical Society, 2010-09-02) Huang, TW; Chen, TK; Yeh, KW; Ke, CT; Chen, CL; Huang, YL; Hsu, FC; Wu, MK; Wu, PM; Avdeev, M; Studer, AJ
    In this paper, we report the results of detailed studies on Mn and Cu substitution to Fe site of β-FeSe, namely, MnxFe1−xSe1−δ and CuxFe1−xSe1−δ (δ equals to 0.03–0.05 based on our neutron-diffraction refinements). The results show that with only 10 at. % Cu doping the compound becomes a Mott insulator. Detailed temperature-dependent structural analyses of these Mn- and Cu-substituted compounds show that the structural transition, which is associated with the changes in the building block FeSe4 tetrahedron, is essential to the occurrence of superconductivity in β-FeSe. © 2010, American Physical Society