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[Ni(pyrdtc)(PPh3)(NCS)] (1), [Ni(pyrdtc)(4-MP)(NCS)] (2), [Ni(pyrdtc)(PPh3)(CN)]·H2O (3), [Ni(pyrdtc)(PPh3)2]ClO4 (4), and [Ni(pyrdtc)(P͡P)]BPh4·2H2O (5) [where pyrdtc: Pyrrolidine carbodithioate/S͡S, PPh3: Triphenylphosphine, 4-MP: Tri(4-methylphenyl)phosphine, dppe/P͡P: 1,2-Bis(diphenylphosphino)ethane] have been prepared from the parent bis-dithiocarbamate, [Ni(pyrdtc)]2 (6). The prepared compounds were characterized by electronic, IR, 1H, 13C, and 31P NMR spectra. In the IR spectra of the compounds, thioureide bands are observed at higher wavenumbers for the mixed ligand complexes 1-5 (1528-1540 cm-1) than the parent compound (1490 cm-1). Cyclic voltammetry showed an increasing order of reduction potentials: 5 << 1 ~ 2 < 3 < 4 << [Ni(pyrdtc)2] indicating an alleviation of electron density on nickel in the mixed complexes compared to the parent compound. Single crystal X-ray structure of the complexes displayed planar geometry around nickel which is in keeping with their diamagnetism. Bond Valence Sums calculated with the corrected Rij indicated the divalent nature of nickel with predominant covalent interactions. Continuous shape measure analysis of the mixed ligand chromophores stipulates a planar square environment around central nickel atom and deviation to tetrahedral or trigonal bipyramidal variants are absolutely negated. In this study, CSM analysis of cis-platin, a clinical anti-cancer agent, showed a comparable shape measure as those of the mixed ligand complexes 1-5. Hence, pyrrolidinecarbodithioate acts as a ‘chuck’ in compounds 1-5 to stabilize the planar square shape of the nickel chromophores and provides a suitable template to synthesize analogues of cis-platin.

Mechanochemical synthesis is an attractive preparative method that combines a green approach with versatility, efficiency, and rapidity of reaction. However, it often yields microcrystalline materi...

The low-temperature structure of ${\mathrm{Bi}}_{0.68}{\mathrm{Ca}}_{0.32}{\mathrm{MnO}}_{3}$ has been solved from electron and neutron diffraction data. The quantitative simultaneous refinement indicates an ordering of the Mn cations in a ``stripe/chess''-like pattern. The ordering is accompanied by the formation of short Mn---Mn distances and the rearrangement of the Mn---O bonds indicating the development of complex extended ``orbital molecules.'' The primary order parameter breaks inversion symmetry and allows the generation of a spontaneous electrical polarization as the secondary order parameter. The neutron data at low temperature indicate the coexistence of a pseudo-CE long-range-ordered structure with a strongly reduced moment and short-range ferromagnetic correlations. These results indicate an intricate competition between the charge, orbital, and magnetic degrees of freedom and the ${\mathrm{Bi}}^{3+}$ stereoactivity in this manganite system.

The crystal structure of the composite crystal Ca0.83CuO2 was investigated by synchrotron powder diffraction at high temperature. The incommensurate modulated structure was firstly analyzed at room temperature (RT) and successfully solved by adopting the (3D + 1)-dimensional symmetry P21/m(&alpha, 0&gamma, )0s. The composite crystal is featured by a non-uniform distribution of Ca ions occupying octahedral sites formed by the spatial arrangement by the infinite 1D CuO2 chains. By approaching 500 K, Ca0.83CuO2 undergoes a structural rearrangement ruled by the shrinking of the Ca interatomic distances. The high-temperature crystalline phase is characterized by a different incommensurate periodicity requiring the recombination of the Ca/CuO2 balance featuring the composite intergrowth of the two almost independent sub-structures. We ascertain that the new crystalline form is stable up to 950 K near to the limit of the thermal decomposition.

WOS: 000519988900002 Martensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in Ni2MnGa, where the martensite transition is at the heart of the striking magnetic shape memory and magnetocaloric properties. Interestingly, the martensitic transformation is preceded by a premartensite phase, and the role of this precursor and its influence on the martensitic transition and properties is still a matter of debate. In this work we report on the influence of Co doping (Ni50-xCoxMn25Ga25 with x = 3 and 5) on the martensitic transformation path in stoichiometric Ni2MnGa by neutron diffraction. The use of the superspace formalism to describe the crystal structure of the modulated martensitic phases, joined with a group theoretical analysis, allows unfolding the different distortions featuring the structural transitions. Finally, a general Landau thermodynamic potential of the martensitic transformation, based on the symmetry analysis, is outlined. The combined use of phenomenological and crystallographic studies highlights the close relationship between the lattice distortions at the core of the Ni2MnGa physical properties and, more in general, on the properties of the martensitic transformations in the Ni-Mn based Heusler systems. Departments of Excellence' program of the Italian Ministry for Education, University and Research (MIUR, 2018-2022) The authors acknowledge the Science and Technology Facilities Council for providing neutron beamtime on the WISH beamline. F.O. acknowledges Dr. Giovanni Romanelli for useful discussion. This work has benefited from the COMPHUB Initiative, funded by the `Departments of Excellence' program of the Italian Ministry for Education, University and Research (MIUR, 2018-2022).

The family of compounds with formula [NH4][M(HCOO)(3)], with M a divalent D-metal, is characterized by porous frameworks hosting NH4+ cations exhibiting at low temperature a spontaneous ferroelectric polarization. The presence of magnetically active divalent metal determines the occurrence of anti-ferromagnetic ordering below 30 K opening the avenue for a rational formulation of a new class of multiferroic materials. We demonstrate that this intriguing class of compounds can be synthetized with a mechanochemical approach. This novel route of synthesis was applied to the series [NH4][M(HCOO)(3)] with M = Cu2+, Co2+, Mn2+, Zn2+ and Ni2+ using as reactants ammonium formate and the corresponding di-hydrated metal formates. The milling duration of the process correlates with the thermal stability of the dihydrated metal formates indicating that the first step of the mechanosynthesis process is represented by the removal of water molecules. The characterizations of the final products indicate the presence of single phase [NH4][M(HCOO)(3)] compounds with an excellent degree of crystallinity. (C) 2021 Elsevier B.V. All rights reserved.

We present a study on the Curie transition of austenitic Ni-Mn-In full Heusler compounds when Mn atoms are replaced by Fe or Cu. The substituted compounds are designed to present a relevant magnetocaloric effect at the second order Curie transition of the austenitic phase near room temperature. We show that Fe and Cu modify the magnetic moments and interactions responsible of the localized magnetism in the L21 ordered cubic structure, resulting in a change of the Curie temperature and saturation magnetization of the compound. Neutron diffraction experiments and electron microscopy analysis were used to study the sites occupancy of doping atoms and the presence of secondary phases, thus possibly optimizing the annealing protocols to obtain homogeneous samples even at high Cu/Fe concentrations. On this basis, a series of quinary compounds with a tunable Curie temperature and high values of saturation magnetization (100-110 Am2/kg at 80 K) was successfully synthesized. The obtained results show the feasible fine tuning of the Curie temperature at which the peak of the magnetocaloric effect is realized, highlighting a new promising strategy to design graded regenerators for room temperature magnetocaloric applications.

We report on the room temperature, simple and cheap preparation by mechano-synthesis of polycrystalline targets of complex sulphide semiconductors, namely CuInS (CIS), to be used for film deposition in physical vacuum techniques such as PLD, sputtering or LT-PED. The sulphur (S)-based targets usually require expensive high pressure equipment to compensate the high S vapour pressure; nevertheless they are indispensable for the deposition of high band-gap semiconductor materials. The comparison of CIS films grown by mechano-synthesis and by commercial targets demonstrates similar material quality, making the mechano-synthesis a viable solution in the fabrication of high band-gap, S-based targets of complex chalcogenides.

This work presents a top-down method, based on ball-milling techniques, for the preparation of Ni 50 Mn 30 Ga 20 and Ni 50 Mn 18.5 Cu 6.5 Ga 25 micro-meter and sub-micro-meter sized particles. The structural, morphological, and magnetic features of the as-milled and annealed particles are investigated. First, we observe a detrimental effect on the magnetic properties and magneto-structural phase transitions of the induced lattice defects and atomic disorder, and second, we demonstrate the possibility to recover the original configuration by subsequent annealing. The optimization of the latter is strongly dependent on the initial milling energy, but, generally, a fast recovery of the Heusler and martensitic phases is observed. Further, we can tune the transformation temperatures or even improve the magnetic properties, in terms of increase of phase homogeneity, decrease of thermal hysteresis and increase of saturation magnetization, by decreasing the particles’ size of the examined compounds.

Tetragonal Mn x Ga 1–x ( x = 0.70, 0.75) thin films grown on SrTiO 3 substrates exhibit perpendicular magnetic anisotropy with coercive fields between 1 and 2 T. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that 40 nm samples grown at 300–350 °C lead to films with the tetragonal c-axis oriented primarily perpendicular to the film plane but with some fraction of the sample exhibiting the c-axis in the film plane. This structure results in an undesirable secondary magnetic component in the out of plane magnetization. Growth at 300 °C with a reduced thickness or Mn concentration significantly decreases the tetragonal c-axis in the film plane.

The stoichiometric Ni$_{50}$Mn$_{25}$In$_{25}$ Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of $x$ = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state., Appearing in Journal of Physics: Condensed Matter

In this work, we highlight the occurrence of different physical mechanisms that independently control the saturation magnetization and the ferro-paramagnetic transition temperature of Ni-Mn-based Heusler compounds, opening new possibilities in mastering the functional properties of this wide class of magnetic materials. We present the magnetic, structural and magnetocaloric features of a complete Ni48Mn36In16−xSnx (x = 0–16) series. The observed different trends of the critical temperature and of the saturation magnetization on varying the Sn to In ratio are discussed with the help of first-principles calculations of the electronic structure and magnetic interactions of the compound.

After cellulose, lignin is the most abundant plant-derived polymer in nature. It provides mechanical support to plants, but it has also a defense role against pests and diseases, thanks to antioxidant, bactericidal, and antifungal properties, deriving from its polyphenolic nature. Huge quantities of technical lignins are obtained during several industrial processes and they actually represent a waste of paper pulp and bioethanol industry. Although in the last decades many efforts have been directed to obtain lignin valorization in several fields and for diverse applications, this biobased polymer is still largely underutilized. In particular, very little is known about the possibility to exploit its antioxidant, antifungal, and antibacterial properties in the agronomical field. On the other hand, pest control is often achieved by using copper-based pesticides, but environmental and health issues urge for novel solutions implying reduced copper content. We here describe novel hybrid organic-inorganic materials obtained by combining copper(II) salts with two types of technical lignins. Cu-containing materials (lignin@Cu) have been characterized by different techniques, including X-ray powder diffraction and transmission electron spectroscopy analyses, revealing nanocrystals of brochantite (Cu4SO4(OH)(6)) grown in the lignin matrix. Lignin@Cu was tested for its antifungal and antibacterial profile against a vast panel of pathogens of agronomical interest. Furthermore, preliminary tests on crops in a greenhouse were performed: lignin@Cu had better performances than a commercial pesticide based on copper(II) hydroxide on tomato plants against Rhizoctonia solani, indicating a great potential of these materials as plant protection products.

We investigate the specific influence of structural disorder on the suppression of antiferromagnetic order and on the emergence of cuprate superconductivity. We single out pure disorder, by focusing on a series of Y$_{z}$Eu$_{1-z}$Ba$_2$Cu$_3$O$_{6+y}$ samples at fixed oxygen content $y=0.35$, in the range $0\le z\le 1$. The gradual Y/Eu isovalent substitution smoothly drives the system through the Mott-insulator to superconductor transition from a full antiferromagnet with N\'eel transition $T_N=320$ K at $z=0$ to a bulk superconductor with superconducting critical temperature $T_c=18$ K at $z=1$, YBa$_2$Cu$_3$O$_{6.35}$. The electronic properties are finely tuned by gradual lattice deformations induced by the different cationic radii of the two lanthanides, inducing a continuous change of the basal Cu(1)-O chain length, as well as a controlled amount of disorder in the active Cu(2)O$_2$ bilayers. We check that internal charge transfer from the basal to the active plane is entirely responsible for the doping of the latter and we show that superconductivity emerges with orthorhombicity. By comparing transition temperatures with those of the isoelectronic clean system we deterime the influence of pure structural disorder connected with the Y/Eu alloy., Comment: 10 pages 11 figures, submitted to Journal of Physics: Condensed Matter, Special Issue in memory of Prof. Sandro Massida

The organometallic unit {[(p-cymene)RuCl2]2[4,4′-bis(diphenylphosphino)biphenylene]} has been revealed to be a good building block for the construction of wheel-and-axle (waa) crystalline scaffolds able to incorporate different organic solvents. In fact, the synthesis carried out in tetrahydrofuran (THF), dichloromethane, toluene, and p-xylene led to the corresponding solvates. An apohost could instead be isolated from diethyl ether. However, this showed a lower crystallinity than the solvates, as usually expected for waa compounds. Thermal extrusion of THF led to a new apohost framework. The desolvation process occurred with partial loss of crystallinity which, however, was completely restored after sorption of THF vapors with rebuilding of the starting THF solvate. THF could also be exchanged with p-xylene by a vapor uptake process, while exposure to other aromatics, such as benzene, toluene, and o- and m-xylene led to partial guest exchanges. The use of a more branched guest, such as p-cymene, complete...

Magnetic shape memory materials hold a great promise for next-generation actuation devices and systems for energy conversion, thanks to the intimate coupling between structure and magnetism in their martensitic phase. Here novel magnetic shape memory free-standing nanodisks are proposed, proving that the lack of the substrate constrains enables the exploitation of new microstructure-controlled actuation mechanisms by the combined application of different stimuli-i.e., temperature and magnetic field. The results show that a reversible areal strain (up to 5.5%) can be achieved and tuned in intensity and sign (i.e., areal contraction or expansion) by the application of a magnetic field. The mechanisms at the basis of the actuation are investigated by experiments performed at different length scales and directly visualized by several electron microscopy techniques, including electron holography, showing that thermo/magnetomechanical properties can be optimized by engineering the martensitic microstructure through epitaxial growth and lateral confinement. These findings represent a step forward toward the development of a new class of temperature-field controlled nanoactuators and smart nanomaterials., M.C. thanks Consorzio Spinner for the direct financial support.

The temperature dependent x-ray diffraction and magnetization measurements on the off stoichiometric Ni2Mn1+xIn1-x alloys have confirmed the appearance of martensite at critical Mn concentration of x=0.35. The high temperature phase of all the alloys have cubic L21 structure with the lattice constant steadily decreasing with increase in Mn concentration. Martensitic transition begins to appear in Ni2Mn1.35In0.65 at about 197K and the structure seems to adopt two phases including the major cubic along with the modulated monoclinic phase. This has been explained on the basis of number of Mn-Ni-Mn hybridized pairs that are responsible for inducing martensitic transition.The temperature dependent x-ray diffraction and magnetization measurements on the off stoichiometric Ni2Mn1+xIn1-x alloys have confirmed the appearance of martensite at critical Mn concentration of x=0.35. The high temperature phase of all the alloys have cubic L21 structure with the lattice constant steadily decreasing with increase in Mn concentration. Martensitic transition begins to appear in Ni2Mn1.35In0.65 at about 197K and the structure seems to adopt two phases including the major cubic along with the modulated monoclinic phase. This has been explained on the basis of number of Mn-Ni-Mn hybridized pairs that are responsible for inducing martensitic transition.

The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing a propagation vector k 1/4 [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material combining ferrielectric properties and a long period antiferromagnetic structure.

The synthesis and structural and magnetic characterizations of K3Fe6F19, a new iron potassium fluoride with a complex tungsten bronze related structure, are presented. This phase was found during the investigation of relatively low-temperature (600 degrees C) synthesis conditions of classical tetragonal tungsten bronze (TTB) fluorides and can be considered an intermediate that forms at this temperature owing to faster crystallization kinetics. The K3Fe6F19 compound has an orthorhombic structure (space group Cmcm (63), a = 7.6975(3) angstrom, b = 18.2843(7) angstrom, c = 22.0603(9) angstrom) related to the TTB one, where the perovskite cage is substituted by a large S-shaped channel simultaneously occupied by two potassium atoms. The magnetic structure, characterized by magnetization measurements on an oriented single crystal and powder neutron diffraction, is dominated by the presence of interconnected double stripes of antiferromagnetic triangular exchange interaction patterns alternately rotated in clock- and anticlockwise fashion. The magnetic order takes place in a wide temperature range, by increasing progressively the interaction dimensionality.

Thin films of Ni-Mn-Ga alloy ranging in thickness from 10 to 100 nm have been epitaxially grown on MgO(1 0 0) substrate. Temperature-dependent X-ray diffraction measurements combined with room-temperature atomic force microscopy and transmission electron microscopy highlight the structural features of the martensitic structure from the atomic level to the microscopic scale, in particular the relationship between crystallographic orientations and twin formation. Depending on the film thickness, different crystallographic and microstructural behaviours have been observed: for thinner Ni-Mn-Ga films (10 and 20 nm), the L2(1) austenitic cubic phase is present throughout the temperature range being constrained to the substrate. When the thickness of the film exceeds the critical value of 40 nm, the austenite-to-martensite phase transition is allowed. The martensitic phase is present with the unique axis of the pseudo-orthorhombic 7M modulated martensitic structure perpendicular to the film plane. A second critical thickness has been identified at 100 am where the unique axis has been found both perpendicular and parallel to the film plane. Magnetic force microscopy reveals the out-of-plane magnetic domain structure for thick films. For the film thickness below 40 nm, no magnetic contrast is observed, indicating an in-plane orientation of the magnetization. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We report on the experimental observation of a long-range antiferromagnetic structure in the metamagnetic Ni-Co-Mn-Ga Heusler alloys. The accurate magnetic symmetry analysis based on experimental neutron diffraction data, exploiting the Shubnikov theory, allows the determination of the correct magnetic space group of the system. A two-step process, featuring the ordering of the Ni and Mn sublattices at different temperatures, leads to the antiferromagnetic structure in martensite. A perfect, constrained by the symmetry, antiferromagnetic ordering of the Ni sublattice in the ``paramagnetic gap'' is observed, followed by the ordering of the Mn sublattice at lower temperatures. The observation of such antiferromagnetic structure clarifies the current debate on the presence of antiferromagnetic interactions in the (Ni,Co)-Mn-$X$ ($X=\mathrm{Ga}$, Sn, Sb, and In) ferromagnetic shape memory alloys and yields new insights in understanding the magnetostructural properties of this relevant class of materials.

The complexes trans-[Ni(4-MP)2(NCS)2]·MeCN (1) and trans-[Ni(3-MP)2(NCS)2] (2) (4-MP = tri(4-methylphenyl)phosphine, 3-MP = tri(3-methylphenyl)phosphine) were prepared and characterized by IR, UV–visible, NMR spectra, CV, TGA and single crystal X-ray crystallography. Both the complexes have planar geometry and are diamagnetic. The Ni–P distances in both complexes are relatively short as a result of strong back donation from nickel to phosphorus. The phenyl rings in the 3-MP analogue (2) show increased pitching with reference to the plane formed by the ipso carbons due to increased steric effects. For complex (2), the N–Ni–N and P–Ni–P angles are significantly lower than the almost linear N–Ni–N and N–Ni–P angles observed for both complex (1) and trans-[Ni(PPh3)2(NCS)2]. This observation indicates that the 3-methylphosphine ligand forces complex (2) to distort towards a tetrahedral geometry. IR spectra of both complexes show strong bands around 2,090 cm−1 due to N-coordinated thiocyanate, while the electronic spectra contain d–d transitions around 452 nm. Cyclic voltammograms show that the irreversible one-electron reduction potentials increase in the following order: trans- [Ni(PPh3)2(NCS)2]

The crystal structure of the modulated, low-temperature martensitic phase in Ni2.41Fe0.59Ga ferromagnetic shape memory alloy (FSMA) has been determined by Rietveld refinement of neutron powder diffraction data. The structure shows an incommensurate modulated crystal lattice with some analogies with the 7 M modulated martensitic structure found in Ni2Mn1.2Ga0.8 Heusler alloy. The observed type of lattice modulation with q = 0.3521c∗ gives rise to a new type of martensitic crystal structure in the FSMAs.

Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different “nM” periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated.

(1,10-Phenanthroline)bis(piperidinecarbodithioato-S,S′)cadmium(II), [Cd(pipdtc)2(1,10-phen)] (1) and (2,2′-bipyridine)bis(piperidinecarbodithioato-S,S′)cadmium(II), [Cd(pipdtc)2(bipy)] (2) adducts were prepared and the crystal structures are reported. Cd–S and Cd–N distances and the angles subtended at cadmium are almost the same in both complexes but the Cd–S distances in the adducts are longer than those in Cd(pipdtc)2 (3) complexes due to the presence of an additional neutral ligand. Thioureide C–N distance in 1 and 2 are supported by νC–N bands observed at 1471 and 1470 cm−1, respectively. S2p binding energies for the adducts show a significant reduction in value compared to the parent dithiocarbamate indicating the weakening of the Cd–S bond on adduct formation. The observed reduction in binding energy is due to the increased electron density on the metal in the adducts. The cyclic voltammetric study on the complexes also show an increase of electron density on cadmium in the adducts compared to Cd(pipdtc)2.

For the first time, the 7M modulated structure, frequently observed in ferromagnetic shape memory Ni–Mn–Ga martensitic phases, is solved by powder diffraction analysis. Two polycrystalline samples with composition Ni2Mn1.2Ga0.8 and Ni2.15Mn0.85Ga, respectively, showing a 7M martensitic state stable at room temperature, were studied. The determination of the modulated crystal structure of Ni2Mn1.2Ga0.8 martensite was achieved by refining the X-ray powder diffraction pattern by the Rietveld method. The basic structure belongs to monoclinic symmetry. The crystal structure, solved within the superspace approach, is found to show an incommensurate 7M modulation with q = 0.308c∗. The Rietveld refinement for Ni2.15Mn0.85Ga martensite on the basis of neutron powder data surprisingly provides a very similar incommensurate 7M structure with the same periodicity and analogous modulation function. The incommensurate structure presents typical displacive modulation with several analogies with the Zhdanov (5, 2 ¯ )2 stacking sequence.

The giant magnetocaloric properties of NiMnGa alloys can be enhanced by suitable composition changes that make structural and magnetic transition temperatures to coincide. In this paper we report results on critical temperatures, magnetic anisotropy, and magnetocaloric effect in Ni- and Mn-rich alloys as a function of composition. A phenomenological phase diagram, useful for the identification by thermomagnetic analysis of magnetic and structural transitions in the vicinity of their coincidence, is proposed. Particular emphasis is given to the discussion of giant magnetocaloric effect of those alloys showing a first order magnetostructural transition, the method of its determination, and the potentialities for applications in the field of magnetic refrigeration.

We have studied the magnetocaloric effect of the (La 0.55 Bi 0.15 )Ca 0.3 MnO 3 perovskite. This material shows interesting magnetic properties such as its saturation magnetic moment per formula unit of 3.44 μ B and a magnetic order temperature of 230 K. Below this temperature neutron diffraction experiments show anti-ferromagnetic contributions in the main ferromagnetic structure. The measured heat capacity exhibits a broad jump centred at the Curie temperature. By increasing the magnetic field, the jump shifts to higher temperatures, confirming the ferromagnetic character of the transition. From the total entropy we have determined the isothermal magnetic entropy (Δ S m ) and the adiabatic temperature change (Δ T ad ). We found that both magnitudes display peaks centred at 230 K with maximum values of |Δ S m | = 1.1 J/K mol and Δ T ad = 2.3 K at 9 T applied field. Isothermal measurements of magnetization allow us, through thermodynamic Maxwell relation, to determine the isothermal magnetic entropy. The temperature dependence of Δ S is similar to that obtained from C p although the values are slightly higher. While these values are modest, it is significant that the magnetocaloric effect extends over a large temperature range, showing a good relative cooling power of 190 J/kg at 3 T applied magnetic field.

The authors regret a typo on page 166 of the paper; the anisotropy (K1) values are in the range of 7-9 × 105 J/m3.

The physical characterization and the extended crystallographic study of the double perovskite system Pb2Mn0.6Co0.4WO6 indicate an improper ferroelectric contribution to the polarization induced by the magnetic ordering. In the paramagnetic phase, the compound displays a centrosymmetric orthorhombic double perovskite structure with the Pmcn1' symmetry. The structure is strongly distorted by the lead stereoactivity. Magnetization measurements show two magnetic transitions at 188 and 9 K, but the time-of-flight neutron diffraction data provide evidence for a long-range magnetic ordering only below the second transition. Quantitative structure refinements combined with a comprehensive symmetry analysis indicate the Pm'c2(1)' magnetic space group to be the adequate symmetry to describe the structural distortions and spin ordering in the ground state of the system. The symmetry implies a coexistence of a spontaneous ferromagnetic moment and a ferroelectric polarization along the orthogonal b- and c-axes, respectively, in the long-range ordered structure. Macroscopic measurements confirm the presence of the spontaneous polarization also below the first transition at 188 K, where only short-range magnetic correlations are evidenced by diffuse scattering in neutron diffraction.

Ferromagnetic martensitic NiMnGa Heusler alloys are promising materials potentially exploitable for the fabrication of microdevices based on novel actuation mechanisms [1]. In bulk materials, giant strains obtainable by magnetomechanical effects based on the twin variant reorientation induced by a magnetic field (MIR), are higher than typical magnetostriction and state-of-the-art piezoelectric values [2]. Moreover, the coupling between magnetic and structural degrees of freedom leads to several multifunctional properties (e.g. "giant" magnetomechanical, magnetocaloric) [3]. Low-dimensional materials, mainly thin films, have recently attracted much interest for the promising applications. With respect to the bulk materials, they offer the further possibility of tuning properties by thickness [4] and by the choice of suitable substrates and underlayers [5]. The present paper is aimed at deepening these effects, also extending the study to laterally confined substrate-constrained and free-standing nanostructures.

Planar nickel(II) complexes involving N-(2-Hydroxyethyl)-N-methyldithiocarbamate, such as [NiX(nmedtc)(PPh3)] (X = Cl, NCS; PPh3 = triphenylphosphine), and [Ni(nmedtc)(P-P)]ClO4(P-P = 1,1-bis(diphenylphosphino)methane(dppm); 1,3-bis(diphenylphosphino)propane (1,3-dppp); 1,4-bis(diphenylphosphino)butane(1,4-dppb) have been synthesized. The complexes have been characterized by elemental analyses, IR and electronic spectroscopies. The increased νC–N value in all the complexes is due to the mesomeric drift of electrons from the dithiocarbamate ligands to the metal atom. Single crystal X-ray structure of [Ni(nmedtc)(1,3-dppp)]ClO4·H2O is reported. In the present 1,3-dppp chelate, the P–Ni–P angle is higher than that found in 1,2-bis(diphenylphosphino)ethane-nickel chelates and lower than 1,4-bis(diphenylphosphino)butane-nickel chelates, as a result of presence of the flexible propyl back bone connecting the two phosphorus atoms of the complex.

Synthesis, spectral and cyclic voltammetric characterization of [Ni(dedtc)(4-MP)2](ClO4) (1), [Ni(dedtc)(4-MP)(NCS)](2), [Ni(dedtc)(PPh3)(NCS)] (3) and [Ni(dedtc)(PPh3)(CN)] (4) (dedtc = diethyldithiocarbamate, 4-MP = tri(4-methylphenyl)phosphine, PPh3 = triphenylphophine) are reported. IR spectra of complexes 1-4 show the characteristic thioureide (C-N) bands at higher wave numbers compared to that of the parent dithiocarbamate complex [Ni(dedtc)2]. The d-d transitions are observed in the region 452—482 nm. The CV studies clearly show the presence of reduced electron density on the nickel ions in mixed ligand complexes 1-4 compared to the parent dithiocarbamate. Single crystal X-ray structure studies show all the complexes to containplanar NiS2P2, NiS2PN, and NiS2PC chromophores in keeping with the observed diamagnetism. In all the complexes the Ni-S distances are asymmetric. The thioureide C-N distance of the complexes 1-4 are less thanthe C-N distance observed in the parent [Ni(dedtc)2]. Synthese, Spektroskopie, Cyclovoltammetrie und Einkristall-Strukturanalysen von planaren NiS2P2-, NiS2PN- und NiS2PC-Chromophoren Es wird uber die Synthese, die spektroskopische und cyclovoltammetrische Charakterisierung von [Ni(dedtc)(4-MP)2](ClO4) (1), [Ni(dedtc)(4-MP)(NCS)] (2), [Ni(dedtc)(PPh3)(NCS)] (3) und [Ni(dedtc)(PPh3)(CN)] (4) (dedtc = diethyldithiocarbamat, 4-MP = Tri(4-methylphenyl)phosphin, PPh3 = Triphenylphosphin) berichtet. Die IR-Spektren der Komplexe 1-4 zeigen die charakteristische Thioharnstoff-(CN)-Bande bei groseren Wellenzahlen verglichen mit dem homoleptischen Dithiocarbamat-Komplex [Ni(dedtc)2]. Die d-d-Ubergange werden im Bereich von 452-482 nm beobachtet. Die CV-Untersuchungen zeigen eine deutlich reduzierte Elektronendichte der Nickelionen in den Gemischtligand-Komplexen 1-4 im Vergleich zu [Ni(dedtc)2]. Nach den Einkristallstrukturanalysen enthalten alle Komplexe planare NiS2P2-, NiS2PN- und NiS2PC-Chromophore, entsprechend ihrem Diamagnetismus. In allen Komplexen sind die Ni—S-Bindungen asymmetrisch. Die Thioharnstoff—CN-Abstande sind in 1-4 kurzer als im Ausgangskomplex [Ni(dedtc)2].

Transition metal fluorides with tetragonal tungsten bronze (TTB) structure, having general formula KxMIIxMIII1-xF3 with 0.4 < x < 0.6 and M belonging to transition metals, have been studied over the past decades because of the frustrated magnetic ordering arising at low temperature. We investigated the structural properties of TTB fluorides by transmission electron microscopy (TEM). The results, coupled with an accurate structure analysis performed by single-crystal XRD on K0.53FeF3, revealed ferroelectricity and a unified structural description of these materials, where charge order and tilt modulations coexist, each one with its own periodicity differently commensurate to the conventional TTB cell. Whereas the charge order is peculiar of the mixed valence fluorides, the nature of the tilt modulation is clearly associable to the structural features of TTB niobates, suggesting also for the fluoride bronzes the existence of a generalized ferroelectric-ferroelastic behavior at room temperature.

AlVO4 is a relatively new sensor material derived from V2O5/Al2O3 mixtures to selectively detect NO and NO2 gases. Previous studies carried out in order to determine its structural, absorptive and sensory properties indicate that the AlVO4 is not the only single phase. This work deals with the synthesis of the compound by the ceramic and the nitrate decomposition methods, and by the sol gel route. The Rietveld refinement of the compound was carried out in order to determine its crystal structure. Single phase of AlVO4 was successfully obtained via the nitrate decomposition and the sol gel methods. Thereafter, films prepared by the sol gel route were deposited on alumina and Si/SiO2/Pt substrates and characterized by SEM and X-ray diffraction. The electric characterization of the AlVO4 on alumina substrate film is also presented.

A one-dimensional polymeric pyridinium chlorocuprate (HPy)2[Cu3Cl8(H2O)2], an intermediate between (HPy)CuCl3 and CuCl2·2H2O, has been synthesized and characterized by X-ray analysis [monoclinic, P21/c, a = 7.8950(10), b = 14.144(2), c = 9.921(10) A, β = 99.20(2)°]. The structure contains [Cu3Cl8(H2O)2]n2n− chains in which both square-pyramidal and octahedral CuII exist. The chains are composed of linked [Cu2Cl6]2− dimers and CuCl2(H2O)2 monomeric units. On being heated in the solid state the compound undergoes dehydration followed by dehydrohalogenation to produce a pyridine complex of CuII: [Cu3Py2Cl6]. Other compounds, (HPy)2[CuCl4], CuPyCl2 and CuPy2Cl2, also produce [Cu3Py2Cl6] as an intermediate on thermal analysis. Magnetic studies reveal ferromagnetic coupling within the chains with an intradimer exchange coupling of 12.1 cm−1 and a dimer-monomer exchange coupling of 1.34 cm−1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The 1,3-dipolar cycloadditions of the cyclic nitrones 2-phenyl-3H-indole-3-one N-oxide (2-phenylisatogen, 1a) and 2-phenyl-3-phenylimino-3H-indole N-oxide (1b) to several electron-deficient alkenes 2a−d are reported. All the reactions studied are highly diastereoselective: the regioisomers with the ethoxycarbonyl group attached to the 4-position of the isoxazolidine moiety are the only products isolated, except in the reactions of nitrones 1a and 1b with ethyl acrylate 2a where mixtures of the two different regioisomers are obtained. Crystal structures of compounds 3b, 5a, 5b, 9a and 10b were determined by X-ray analysis, while the structure of the other cycloadducts was determined by spectroscopic analysis. Ab initio calculations were carried out showing that product distribution may be influenced by kinetic rather than thermochemical factors. Ab initio calculations of the 1H NMR shielding tensor were performed on compounds 3b, 4b, 5a and 6b and the chemical shifts obtained are in perfect agreement with the experimental ones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

KTiOPO 4 single crystals doped with trivalent impurity ions of chromium were grown by spontaneous nucleation and seeded growth techniques. Structural refinement performed on the grown crystals by single crystal X-ray diffraction technique reveals that chromium ions occupy both the potassium sites with different filling coefficients. Incorporation of Cr 3+ causes the absorption edge in the UV spectrum to shift towards the lower energy. The dependence of optical absorption coefficient with the incident photon energy in the UV–VIS region has been discussed. Optical and SEM studies indicate the existence of two-dimensional nucleation mechanisms.

Ni-Mn based Heusler alloys are of considerable interest due to their multifunctional properties such as magnetic shape memory, magnetocaloric effect and spintronics. The reason for these multifunctional properties is the presence of a first order martensitic transition and its strong coupling to the magnetization. In this work, one of the outstanding class of martensitic Heuslers, Ni-Mn-Sn, is investigated in relation to magneto-structural phase transitions and the stability of the various crystallographic structures under varying temperature. Temperature-dependent X-ray diffraction, resistance and magnetization measurements on Ni50Mn50-xSnx alloys are performed in a broad valence electron concentration range 7.91

The synthesis and crystal structure of thermochromic, yellow benzimidazolium tetrachlorocuprate(II), (C7H7N2)2CuCl4 (1), have been reported. The compound crystallizes in the C 2/c space group and contains discrete tetrahedral CuCl4 2� species. It absorbs one molecule of water from humid atmosphere at room temperature to produce a hydrated green form, (C7H7N2)2CuCl4/H2O, which upon heating loses the water molecule in two steps to form the anhydrous yellow compound 1. The role of the water molecule on the solid state, yellow v/green thermochromic transformation is discussed. # 2002 Elsevier Science Ltd. All rights reserved.

The new title compound is prepared by solid state reaction of a stoichiometric mixture of PbO, MnCO3, and WO3 (N2 stream, 800 °C for 2 h and 820 °C for 4 h).