ABSTRACT
Hadal trenches are unique geological and ecological systems located along subduction zones. Earthquake-triggered turbidites act as efficient transport pathways of organic carbon (OC), yet remineralization and transformation of OC in these systems are not comprehensively understood. Here we measure concentrations and stable- and radiocarbon isotope signatures of dissolved organic and inorganic carbon (DOC, DIC) in the subsurface sediment interstitial water along the Japan Trench axis collected during the IODP Expedition 386. We find accumulation and aging of DOC and DIC in the subsurface sediments, which we interpret as enhanced production of labile dissolved carbon owing to earthquake-triggered turbidites, which supports intensive microbial methanogenesis in the trench sediments. The residual dissolved carbon accumulates in deep subsurface sediments and may continue to fuel the deep biosphere. Tectonic events can therefore enhance carbon accumulation and stimulate carbon transformation in plate convergent trench systems, which may accelerate carbon export into the subduction zones.
ABSTRACT
We present here the results of low-temperature magnetization and X-ray magnetic circular dichroism studies on the single crystals of BaFe12O19 which reveal for the first time the emergence of a spin glass phase, in coexistence with a long-range ordered ferrimagnetic phase, due to the freezing of the basal plane spin component.
ABSTRACT
A new multiferroic solid solution [Formula: see text] has been developed and characterized for structure, phase transition, magnetoelectric and magnetoelastic coupling. Temperature dependent measurement of dc-magnetization [Formula: see text] on [Formula: see text] ceramic shows two magnetic transitions one around [Formula: see text]42 K and the second at [Formula: see text]130 K. The real part of dielectric permittivity exhibits step like change at the magnetic anomaly temperature ([Formula: see text]130 K) which indicates the presence of magnetoelectric coupling. The change in the value of dielectric permittivity on the application of magnetic field confirms the presence of magnetoelectric coupling in [Formula: see text] ceramic. The room temperature polarization (P)-electric field (E) hysteresis loop measurement shows week ferroelectric nature of sample while the magnetization (M) versus magnetic field (H) measurement suggest weakly ferromagnetic character. The ferroelectric nature of sample was further confirmed by calculating remanent polarization using PUND measurement. The Rietveld structural analysis of low temperature x-ray powder diffraction data does not reveal any crystallographic phase transition in terms of peak splitting or new reflections. However, temperature dependence of lattice parameters, tetragonality, unit cell volume, [Formula: see text] octahedral tilt angle ([Formula: see text]), [Formula: see text] bond length and [Formula: see text] bond angles reveal discontinuous changes at both the magnetic transitions observed in temperature dependence of magnetization. This confirms that both the magnetic anomalies (around [Formula: see text]42 K and [Formula: see text]130 K) exhibit magnetoelastic coupling accompanied with isostructural transitions.
ABSTRACT
The tectonic evolution of Laxmi basin, presently located along western Indian passive margin, remains debated. Prevailing geodynamic models of Laxmi basin include two mutually competing hypotheses, culminating in either a hyper-stretched continental crust or an oceanic crust overlying an extinct spreading centre. The longstanding conundrum surrounding its precise crustal affinity precludes a complete understanding of the early opening of the Indian Ocean. Here, we present distinct geochemical and geophysical imprints from the igneous crust in Laxmi basin obtained through International Ocean Discovery Program Expedition 355. The geochemical and isotopic signatures of the Laxmi basin crust exhibit uncanny similarities with forearc tectonic settings. Our observations imply a relict subduction initiation event occurred in the Laxmi basin in the Late Cretaceous-Early Cenozoic that marks a significant Cenozoic plate reorganisation record in the northwest Indian Ocean. New findings therefore warrant re-evaluation of the Gondwana breakup to account for the nascent subduction in the northwest Indian Ocean.
ABSTRACT
Le Bail and Rietveld analysis of high resolution synchrotron x-ray powder diffraction (SXRPD) data shows unambiguous signatures of the failure of the commensurate 3M modulation model. Using (3 + 1) dimensional superspace group formalism, we have not only confirmed the incommensurate modulation in the premartensite phase with a modulation wavevector of q = 0.337 61(5)c* but also determined the superspace group (Immm(00γ)s00), atomic positions and amplitude of modulations for the incommensurate premartensite phase of Ni2MnGa for the first time. Our results may have important implications in the understanding of the martensitic transition and hence the magnetic field induced strains.
ABSTRACT
We compare the effectiveness of various known organometallic transesterification catalysts with a novel SnCl(2)·2H(2)O transesterification catalyst in the formation of homogeneous PC/PMMA blends with single T(g). It is shown that SnCl(2)·2H(2)O works more efficiently than the other organometallic transesterification catalysts. Even 0.1% (wt/wt) of SnCl(2)·2H(2)O is enough to establish an interaction between PC and PMMA phases, leading to the formation of a homogeneous PC/PMMA blend with single T(g) and single degradation temperature. FTIR, (1)H NMR, and XRD studies provide evidence of the formation of PC-g-PMMA graft copolymer, which acts as a compatibilizer between the PC and PMMA phases. A significant improvement in the optical transparency of the PC/10PMMA blend prepared using SnCl(2)·2H(2)O catalyst as compared with PC/10PMMA without any catalyst is observed. There is also a change in the morphology from granular in uncompatibilized blends to lamellar in the compatibilized blends.
Subject(s)
Polycarboxylate Cement/chemistry , Polymethyl Methacrylate/chemistry , Tin Compounds/chemistry , Catalysis , TemperatureABSTRACT
Nanocrystalline powders of Zn(1-x)Co(x)O synthesized by the coprecipitation technique show anomalous anisotropic broadening for x>0.05. This peak broadening is shown to be not only due to a reduction in the particle size but also due to a significant strain contribution, as confirmed by Williamson-Hall analysis. The presence of grouped Co(2+) ions, revealing the presence of clusters of high spin Co(2+) with antiferromagnetically coupled spins, as indicated by magnetization studies, seems to be responsible for the strain.
ABSTRACT
Magnetic, dielectric and calorimetric studies on 0.9BiFeO3-0.1BaTiO3 indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic Tc due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous, atomic level evidence for magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO3-based system.
ABSTRACT
The morphotropic phase boundary in the phase diagram of the technologically important Pb(ZrxTi1-x)O3 (PZT) ceramics has been traditionally believed to separate ferroelectric tetragonal and rhombohedral phase regions. This old picture has come under close scrutiny during the last eight years following the discovery of new monoclinic phases in the Cm and Cc space groups. This article presents a brief overview of these discoveries in which the use of multiple diffraction probes (X-ray, electron, neutron diffraction) in conjunction with physical property measurements has played a crucial role. A new phase diagram of PZT showing the stability fields of these structures below room temperature is also presented.
ABSTRACT
An analytical expression for the characteristic length scale (L) of the pair correlation functions for randomly faulted hexagonal close-packed structures is derived for the case when the roots of the characteristic equation are all real. The values of L obtained by this analytical treatment are in good agreement with those obtained numerically.
ABSTRACT
Monte Carlo simulations and analytical results are used to demonstrate that the hexagonal close-packed (h.c.p.) pair correlation functions for different values of randomly distributed growth and deformation faults can be collapsed into master curves when plotted against a spatial variable, scaled with respect to a characteristic length (L). The functional dependences of L on different types of faults are found to be non-universal. A simple method for the determination of L from the measured intensity distributions is also outlined.
ABSTRACT
Results of a powder x-ray diffraction study are presented to show that the so-called 'nearly cubic' phase region of Sr(1-x)Ca(x)TiO(3), in fact, corresponds to two different types of crystal structures. The 'nearly cubic' phase occurring in the composition range 0.35
ABSTRACT
The phase transition behaviour of two 'nearly cubic' compositions, x = 0.40 and 0.43, of Sr(1-x)Ca(x)TiO(3), representative of Pbnm and Pbcm space group structures, has been investigated using temperature dependent dielectric, x-ray diffraction and Raman scattering techniques. For x = 0.40, a first order antiferroelectric phase transition occurs around 364 K followed by an antiferrodistortive phase transition involving the R point ([Formula: see text]) instability at â¼800 K. For x = 0.43, on the other hand, there is no antiferroelectric phase transition. Instead, two antiferrodistortive transitions around 463 and 850 K linked with the M ([Formula: see text]) and R ([Formula: see text]) point instabilities, respectively, are observed. Both the compositions also exhibit qualitatively different types of phase transitions below room temperature. Evidence for a new phase transition at low temperatures is presented for x = 0.43.
