Temperature X-ray Powder Diffraction Data Research Articles

Magnetic and magneto caloric properties of melt-spun rare earth intermetallic compound DyAl2

Laves phase rare earth intermetallic compound DyAl2 has been prepared by melt-spinning under argon atmosphere. The melt-spun DyAl2 sample is crystalline (cubic structure, space group Fd-3m) and is nanostructured. The crystallite size of melt-spun DyAl2 calculated from the room temperature powder X-ray diffraction data is about 23 nm. Transmission electron microscopy image reveals particles of average size, 14 nm. The melt-spun DyAl2 undergoes a paramagnetic to ferromagnetic transition at ∼29 K (TC). This value is about 32 K lower than the ferromagnetic transition temperature of DyAl2 sample prepared by conventional arc-melting technique. Magnetization of the melt-spun DyAl2 does not saturate at 2 K in field of 70 kOe. Magnetic entropy change near TC has been calculated using the field dependent magnetization data. The maximum value of isothermal magnetic entropy change (ΔSm) of melt-spun DyAl2 is ∼ -10.5 Jkg−1K-1 at 30 K for a field change of 70 kOe. The ΔSmvalue is as large as -24 Jkg−1K-1 at 63 K for the arc-melted DyAl2 compound for the same field change. The formation of nanograins upon melt-spinning has led to the reduction of TC as well as the magnetocaloric effect around TC.

Mn-site doping and its effect on inverted hysteresis and thermomagnetic irreversibility behavior of antiferromagnetic Mn5Si3 alloy

The structural and magnetic behavior of Mn-site doped intermetallic manganese silicide alloys of nominal compositions Mn5−xAxSi3 (x = 0.05, 0.1, 0.2 and A = Ni, Cr) have been investigated with a focus to the inverted hysteresis behavior and thermomagnetic irreversibility. Room temperature x-ray powder diffraction data confirm that all the doped alloys crystallize in hexagonal D88 type structure with space group P63/mcm. The doped alloys are found to show paramagnetic–collinear antiferromagnetic (AFM2)–noncollinear antiferromagnetic (AFM1) transitions during cooling from room temperature. A significant decrease in the critical values of both AFM1–AFM2 transition temperatures and fields have been observed with the increasing Ni/Cr concentration. Inverted hysteresis loop, field-induced arrest, and thermomagnetic arrest, the key features of the undoped Mn5Si3 alloy, are found to be significantly affected by the Mn-site doping and eventually vanishes with 4% doping.

Effect of non-magnetic Ag-doping on magnetic and magnetofunctional properties of MnNiGe alloy

Systematic investigations on Ag-doped MnNiGe alloys of nominal compositions MnNi1−xAgxGe (x = 0.10, 0.15 and 0.20) have been performed through dc magnetic measurements in ambient as well as in high pressure conditions. All the Ag-doped alloys undergo martensitic type structural phase transition with a monotonic decrease in transition temperature with increasing Ag concentration. Room temperature x-ray powder diffraction data confirm the presence of both hexagonal and orthorhombic phase for 10% Ag-doped alloy whereas, 15% and 20% Ag-doped alloys are found to be purely hexagonal in nature. Gradual incorporation of ferromagnetic interaction with increasing Ag-concentration in otherwise antiferromagnetic alloy is clear from the magnetic investigations. Application of external hydrostatic pressure further favors ferromagnetism. In addition, these Ag-doped alloys also show a reasonably high magnetocaloric effect around the magnetic and structural transition temperatures which makes these alloys important for magnetic cooling applications. The robustness of the observed magnetocaloric properties have also been checked by high pressure measurements.

Investigation of new magnetoelastic and magnetic transitions accompanied with magnetoelectric coupling in multiferroic

A new multiferroic solid solution has been developed and characterized for structure, phase transition, magnetoelectric and magnetoelastic coupling. Temperature dependent measurement of dc-magnetization on ceramic shows two magnetic transitions one around 42 K and the second at 130 K. The real part of dielectric permittivity exhibits step like change at the magnetic anomaly temperature (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 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, octahedral tilt angle (), bond length and bond angles reveal discontinuous changes at both the magnetic transitions observed in temperature dependence of magnetization. This confirms that both the magnetic anomalies (around 42 K and 130 K) exhibit magnetoelastic coupling accompanied with isostructural transitions.

Trimers of MnO6 octahedra and ferrimagnetism of Ba4NbMn3O12

Ba4NbMn3O12 is reported, synthesized by a solid state method in air. The crystal structure, determined by performing refinements on room temperature powder x-ray diffraction data by the Rietveld method, consists of Mn3O12 trimers in the configuration of three face-sharing MnO6 octahedra, with the trimers arranged in triangular planes. An effective moment of 4.82 μB/f.u is observed and competing antiferromagnetic and ferromagnetic interactions between Mn ions are inferred from the Weiss temperature of −4 K and the ferrimagnetic ordering transition of approximately 42 K. Ba4NbMn3O12 is a semiconductor with a transport activation energy of 0.37 eV.

Tuning ferromagnetism and spin state in [formula omitted]CoO3 ([formula omitted] Sr, Ca) nanoparticles

We investigate the structural, magnetic susceptibility, isothermal magnetization, and electronic properties of La(1−x)AxCoO3 (A= Sr, Ca; x= 0–0.2) nanoparticles. The Rietveld refinement of room temperature powder x-ray diffraction data shows that all the samples crystallize in the rhombohedral structure (space group R3¯c). We observe a significant increase in the ferromagnetic transition temperature as well as in the spontaneous magnetic moment with Sr/Ca substitution at the La site. Interestingly, the coercive field HC decreases/increases with Sr/Ca substitution [4.4 and 13.2 kOe for x= 0.2 (Sr) and 0.2 (Ca) samples, respectively] as compared to the x= 0 sample (7 kOe). X-ray photoemission spectra of core-levels confirm the oxidation state of the constituent elements. Moreover, we demonstrate that the Sr/Ca substitution increases the population of intermediate-spin (IS) and low-spin (LS) states of Co3+ and Co4+ ions, respectively; which tune the ferromagnetism in nanoparticles via double-exchange interaction. More importantly, the contribution of IS states of Co3+ ions and induced strain are significantly larger in Sr substituted samples than in Ca samples, which favours the interpretation of a Jahn-Teller distortion in the Sr samples. This is consistent as in contrast to Ca samples, the magnetic behavior of La(1−x)SrxCoO3 nanoparticles is significantly different than the counterpart bulk samples having same substitution level. Our results suggest the important role of hole carriers, induced strain and nano-size effect in tuning the spin-state and magnetism in La(1−x)AxCoO3 nanoparticles.

Effect Of La And Pb Substitution On Structural And Electrical Properties Of Parent And La/Pb Co Doped BiFeO3 multiferroic

La/Pb co-doped BiFeO3 compounds were prepared by a solid-state reaction. X-ray diffraction of BiFeO3 (BFO), Bi0.725La0.1Pb0.175FeO3 [BLPFO] showed single phase in nature. BFO crystallize in the rhombohedral distorted perovskite structure (space group-R3c) while to that BLPFO crystallize in distorted pseudocubic (Pm-3m) symmetry which has been confirmed by the Rietveld refinement of the room temperature X-ray powder diffraction data. The effect of La/Pb substitution on dielectric constant, and loss tangent, of the samples was studied at room temperature in a wide range of frequency 10 Hz – 1 MHz. The room temperature dielectric constant of BFO (BLPFO) was 120 (200). Ferroelectric measurement reveals remnants polarization of BLPFO is about 0.24 μC/cm 2 at an applied field of 15 kV/cm. Weak ferroelectric effect is observed for co-doped BiFeO3 compound.

The First Halide-Free Bimetallic Aluminum Borohydride: Synthesis, Structure, Stability, and Decomposition Pathway

Interaction of solid KBH4 with liquid Al(BH4)3 at room temperature yields a solid bimetallic borohydride KAl(BH4)4. According to the synchrotron X-ray powder diffraction, its crystal structure (space group Fddd, a = 9.7405(3), b = 12.4500(4), and c = 14.6975(4) A) contains a substantially distorted tetrahedral [Al(BH4)4]− anion, where the borohydride groups are coordinated to aluminum atoms via edges. The η2-coordination of BH4 − is confirmed by the infrared and Raman spectroscopies. The title compound is the first aluminum-based borohydride complex not stabilized by halide anions or by bulky organic cations. It is not isostructural to bimetallic chlorides, where more regular tetrahedral AlCl4 − anions are present. Instead, it is isomorphic to the LT phase of TbAsO4 and can be also viewed as consisting of two interpenetrated dia-type nets where BH4 ligand is bridging Al and K cations. Variable temperature X-ray powder diffraction, TGA, DSC, and TGA-MS data reveal a single step of decomposition at 160 °C, with an evolution of hydrogen and some amount of diborane. Aluminum borohydride is not released in significant amounts; however, some crystalline KBH4 forms upon decomposition. The higher decomposition temperature than in chloride-substituted Li−Al (70 °C) and Na−Al (90 °C) borohydrides suggests that the larger alkali metal cations (weaker Pearson acids) stabilize the weak Pearson base, [Al(BH4)4]−.

High temperature X-ray studies of mayenite synthesized using the citrate sol–gel method

Abstract Room temperature and high temperature x-ray powder diffraction and differential thermal analysis/thermo-gravimetric analysis (DTA/TGA) have been used to characterize the phase evolution of bulk mayenite (Ca 12 Al 14 O 33 ) prepared using the citrate sol–gel method. These studies have shown that single phase mayenite forms at 900 °C in air after approximately three hours. High temperature x-ray powder diffraction data show that when firing in air at temperatures 600 °C and below only amorphous content is observed; above 600 °C CaCO 3 is the first phase to crystallize. For samples quenched at 800 °C and evaluated using room temperature x-ray powder diffraction mayenite, CaAl 2 O 4 , and CaCO 3 were present. High temperature x-ray diffraction data collected while firing in 4% H 2 /96% N 2 reveals that CaCO 3 does not form and Ca 12 Al 14 O 33 starts to form around 850 °C. DTA/TGA data collected either in a nitrogen environment or air on samples synthesized using the citrate gel method support the complete decomposition of metastable phases and the formation of mayenite at 900 °C, although the phase evolution is different depending on the environment.

Magnetic And Dielectric Properties Of Multiferroic BiFeO3 nanoparticles Synthesized By A Novel Citrate Combustion Method

Single phase BiFeO3 nanoparticles have been successfully synthesized for the first time by a novel citrate combustion method without using any solvent. Well mixed metal nitrates along with citric acid which is used as fuel combust to give BiFeO3 nanoparticles after annealing. These particles are single phase in nature and crystallize in the rhombohedral distorted perovskite structure (space group-R3c) which has been confirmed by the Rietveld refinement of the room temperature powder x-ray diffraction data. Nearly spherical particles of average particle size 47 nm have been seen from transmission electron micrograph. Room temperature magnetic hysteresis measurement shows weak ferromagnetism though the magnetization does not saturate upto 1.75 T applied field. The coercive field value is calculated to be 180 Oe which is 3 times higher than that prepared by solvent free combustion method using glycine. 57 Fe Mössbauer spectrum can be fitted with a sextet corresponding to single magnetic state of hyperfine field about 49.5 T corresponding to Fe 3+ state of the iron atom. The dielectric relaxation and ac conductivity as a function of frequency have been discussed. High dielectric permittivity has not been found in these nanoparticles like other reported BiFeO3 ceramics.

Vacuum Encapsulated Synthesis of 11.5 K NbC Superconductor

Bulk polycrystalline NbC samples are synthesized through solid state reaction route in an evacuated sealed quartz tube. Studied NbC samples are crystallized in NaCl-type cubic structure with space group Fm-3m. To control cell parameters and minute unreacted phases, different samples are synthesized with various heat treatments. Finally, phase pure NbC is achieved. The grain size of the as systemized material being seen from SEM (scanning electron microscopy) is nonuniform of around 3–10 µm size. Crystal structure and lattice parameters of samples have been calculated by Rietveld analysis of room temperature X-ray powder diffraction data. The lattice parameter increases with synthesis temperature and scales with superconducting transition temperature (T c ). Both AC and DC magnetization exhibited highest T c at around 11.5 K for an NbC sample with lattice parameter a=4.471 Å. The lower critical field (H c1) and irreversibility field (H irr) measured at 3 K are around 250 Oe and 4.5 kOe, respectively. The upper critical field (H c2) being determined from in-field AC susceptibility measurements is 7.8 kOe and 11.7 kOe with 50 % and 90 % diamagnetism criteria, respectively.

Phase coexistence in NaNb(1−x)TaxO3 materials with enhanced dielectric properties

NaNb(1−x)TaxO3 (0.1 ≤ x ≤ 0.9) materials have been synthesized and investigated by combining diffraction methods and high resolution electron microscopy with dielectric measurements. The stabilization of lead-free ferroelectric materials has been established from a threshold dopant composition of 40%, probing the doping process in the B-cationic sublattice of the perovskite structure to be a suitable approach for tuning the dielectric properties of the antiferroelectric NaNbO3 oxide. Rietveld analysis of the room temperature powder X-ray diffraction data for ferroelectric compositions has provided unambiguous evidence for the coexistence of two different orthorhombic phases with lattice parameters a ≈ c ≈ √2ac, b ≈ 2ac in the 0.4 ≤ x ≤ 0.6 composition range, a non-centrosymmetric ferroelectric phase (P21ma) and a centrosymmetric paraelectric phase (Pcmn). The change in the order of the phase transitions from first order-like to second order seems to be related to the coexistence of ferroelectric and paraelectric phases, with the NaNb(1−x)TaxO3 (0.4 ≤ x ≤ 0.6) materials showing an enhanced dielectric response.

Enhanced stability and local structure in biologically relevant amorphous materials containing pyrophosphate

There is increasing evidence that amorphous inorganic materials play a key role in biomineralisation in many organisms, however the inherent instability of synthetic analogues in the absence of the complex in vivo matrix limits their study and clinical exploitation. To address this, we report here an approach that enhances long-term stability to >1 year of biologically relevant amorphous metal phosphates, in the absence of any complex stabilisers, by utilising pyrophosphates (P2O74−); species themselves ubiquitous in vivo. Ambient temperature precipitation reactions were employed to synthesise amorphous Ca2P2O7.nH2O and Sr2P2O7.nH2O (3.8 < n < 4.2) and their stability and structure were investigated. Pair distribution functions (PDF) derived from synchrotron X-ray data indicated a lack of structural order beyond ∼8 A in both phases, with this local order found to resemble crystalline analogues. Further studies, including 1H and 31P solid state NMR, suggest the unusually high stability of these purely inorganic amorphous phases is partly due to disorder in the P–O–P bond angles within the P2O7 units, which impede crystallization, and to water molecules, which are involved in H-bonds of various strengths within the structures and hamper the formation of an ordered network. In situ high temperature powder X-ray diffraction data indicated that the amorphous nature of both phases surprisingly persisted to ∼450 °C. Further NMR and TGA studies found that above ambient temperature some water molecules reacted with P2O7 anions, leading to the hydrolysis of some P–O–P linkages and the formation of HPO42− anions within the amorphous matrix. The latter anions then recombined into P2O7 ions at higher temperatures prior to crystallization. Together, these findings provide important new materials with unexplored potential for enzyme-assisted resorption and establish factors crucial to isolate further stable amorphous inorganic materials.

Synthesis and structure determination of ferromagnetic semiconductors LaAMnSnO6(A = Sr, Ba)

LaAMnSnO6 (A = Sr, Ba) have been synthesized by high temperature solid-state reactions under dynamic 1% H2/Ar flow. Rietveld refinements on room temperature powder X-ray diffraction data indicate that LaSrMnSnO6 crystallizes in the GdFeO3-structure, with space groupPnma and, combined with transmission electron microscopy, LaBaMnSnO6 in Imma. Both space groups are common in disordered double-perovskites. The Mn3+ and Sn4+ ions whose valence states were confirmed by X-ray absorption spectroscopy, are completely disordered over the B-sites and the BO6 octahedra are slightly distorted. LaAMnSnO6 are ferromagnetic semiconductors with a TC = 83 K for the Sr- and 66 K for the Ba-compound. The title compounds, together with the previously reported LaCaMnSnO6 provide an interesting example of progression from Pnma to Imma as the tolerance factor increases. An analysis of the relationship between space group and tolerance factor for the series LaAMnMO6 (A = Ca, Sr, Ba; M = Sn, Ru) provides a better understanding of the symmetry determination for double perovskites.

The restrained Rietveld refinement of modulated trivalent metal polyphosphates M(PO3)3

Abstract Room temperature X-ray powder diffraction data were used to investigate modulated crystal structures of two monoclinic polyphosphates of crystal form C, In(PO3)3 and Y(PO3)3, by the Rietveld refinement. The structures were refined with the program JANA2006 in the superspace groups Xc(0β0)0, β = 1/3, for commensurately modulated In(PO3)3, and Cc(0β0)0, β = 0.36564(7), for incommensurately modulated Y(PO3)3. The positional modulations were described with the first-order harmonic functions. The Rietveld refinement was performed with soft restraints on bond lengths and valence angles in PO4 tetrahedra, as well as on angles in MO6 octahedra. No initial information about modulation parameters was used. A good agreement of the observed and calculated intensities of main and satellite reflections was achieved for both compounds. Obtained modulated structures of In(PO3)3 and Y(PO3)3 are close to published single crystal data.

Large magnetic entropy change in nanocrystalline Pr0.7Sr0.3MnO3

Nanocrystalline Pr0.7Sr0.3MnO3 sample has been prepared by sol-gel method. The room temperature powder x-ray diffraction data show single phase nature of the sample and confirm the cubic crystal structure with Fm3¯m space group. The average crystallite size is calculated using Scherrer formula, and it is found to be ∼25 nm. Transmission electron microscopy image shows that the particles are spherical in shape and the average particle size is ∼35 nm. The sample undergoes ferromagnetic ordering at 235 K (TC) and obeys the Curie–Weiss law in the paramagnetic region. The maximum value of the magnetic entropy change |ΔSM|max is ∼6.3 J kg−1 K−1, and the relative cooling power is ∼385 J kg−1 for a field change of 50 kOe. The Arrott plot confirms that the magnetic ordering is of second order nature. The experimentally observed magnetic entropy change of the sample obeys Landau theory of phase transition well.

Metal to Semimetal Transition in CaMgSi Crystals Grown from Mg−Al Flux

Single crystals of CaMgSi were produced using the metal flux synthesis method in a Mg/Al 1:1 mixture. The large rod-shaped crystals measure up to 7 mm in length. This phase crystallizes with the orthorhombic TiNiSi structure type (space group Pnma; a = 7.4752(2) Å, b = 4.42720(10) Å, c = 8.3149(2) Å; R1 = 0.021). Despite its relationship to semiconducting Zintl phases Mg2Si and Ca2Si, CaMgSi is metallic at room temperature; this produces a positive (∼160 ppm) 29Si MAS NMR chemical shift and is supported by DOS calculations. A metal to semimetal electronic transition at around 50 K is evident in the resistivity, magnetic susceptibility, and electron paramagnetic resonance measurements. Low temperature powder X-ray diffraction data indicates that a structural distortion accompanies this transition. The electronic heat capacity coefficient (0.4695 mJ/mol·K2) determined from low temperature heat capacity data supports the designation of CaMgSi as a semimetal at low temperature. The hydrogen storage capacity of this phase is negligible (≤0.5 wt % hydrogen), although exposure to hydrogen does destabilize the structure, inducing decomposition at 500 °C.

Structural and impedance spectroscopic studies on PbZr xTi 1−xO 3 ceramics

Polycrystalline samples of PbZr x Ti 1− x O 3 [PZT] ceramics (where x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been synthesized by a high temperature solid-state reaction technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies have been carried out to determine the structural phase present and morphological modifications that occur with the change in Zr/Ti ratio. The structural phase evolution studies were carried out from the analysis of room temperature X-ray powder diffraction data. The particle sizes of the powders have been estimated from the width of Bragg's peak using Scherrer formula. Microstructural studies for all the samples have been carried out using SEM. The SEM analysis of the samples showed nearly uniform grain distribution i.e. uniform microstructure with no abnormal grain growth. Impedance measurements have been carried out in the temperature range from room temperature (RT) to 560 °C in the frequency range (5 Hz–13 MHz). AC conductivity has been obtained from this data. The values of activation energy have been obtained from the slopes of the Arrhenius plots.

Effect of hole doping and antiferromagnetic coupling on the itinerant ferromagnetism of [formula omitted] through Cu substitution at Ru site

Systematic studies on the structural, transport and magnetic properties of SrRu 1− x Cu x O 3 ( x = 0.0 – 0.2 ) compounds have been performed. SrRu 0.8Cu 0.2O 3 shows a tetragonal structure unlike the other compositions which exhibit a pseudo-cubic structure. Low temperature powder X-ray diffraction data of SrRu 0.8Cu 0.2O 3 collected at a synchrotron beam line reveals that the tetragonal structure is stable down to 8 K. Ferromagnetic transition temperatures ( T c ) are significantly reduced from 160 to 34 K with Cu doping. All the compositions exhibit irreversibilities in M ZFC( T) and M FC( T) curves ascribable to the presence of domain structures. Magnetic susceptibility measurements show that the copper ions are anti-ferromagnetically coupled for concentrations higher than x = 0.16 . The antiparallel arrangement of Ru 5+ ions with its neighboring cations also contributes to the large reduction in the observed magnetic moment. X-ray photoemission spectroscopy measurements show evidence for both tetravalent and pentavalent Ru ions while copper is in a divalent state. We conclude from our resistivity data that Cu 2+ substitution promotes a polaronic type of conductivity.

Oxide ion distribution and conductivity in Bi 7Nb 2 − 2 xY 2 xO 15.5 − 2 x

A detailed investigation using X-ray and neutron powder diffraction as well as ac impedance spectroscopy in the substituted bismuth oxide system Bi 7Nb 2 − 2 x Y 2 x O 15.5 − 2 x is presented. Combined refinement of variable temperature X-ray and neutron powder diffraction data reveal both compositional and temperature dependencies of the oxide ion distribution in this system. Oxide ions are found to be distributed over three crystallographically distinct sites, with one site exclusively associated with the dopant cations Nb 5+ and Y 3+ leading to a distorted octahedral geometry for these ions. Changes in the oxide ion distribution are correlated with a non-linear thermal expansion as well as non-Arrhenius behaviour of total conductivity at high temperatures.