We suggest, and demonstrate, a systematic approach to the study of cuprate superconductors, namely, progressive change of ion size in order to systematically alter the interaction strength and other key parameters. R(Ba,Sr)2Cu3Oy (R={La,…,Lu,Y}) is such a system where potentially obscuring structural changes are minimal. We thereby systematically alter both dielectric and magnetic properties. Dielectric fluctuation is characterized by ionic polarizability while magnetic fluctuation is characterized by exchange interactions measurable by Raman scattering. The range of transition temperatures is 70-107 K, and we find that these correlate only with the dielectric properties, a behavior which persists with external pressure. The ultimate significance may remain to be proven, but it highlights the role of dielectric screening in the cuprates and adds support to a previously proposed novel pairing mechanism involving exchange of quantized waves of electronic polarization.

High-resolution X-ray diffraction technique, employing a three-crystal monochromator–collimator combination is used to study the irradiation induced defects in flux grown Sr-hexaferrite crystals irradiated with 50 MeV Li 3+ ion beams at room temperature with a fluence value of 1 × 10 14 ions/cm 2 . The diffraction curves of the irradiated crystals suggest the possibility of creation of low angle grain boundaries and other point/clusters of defects causing amorphization in the irradiated crystals. The perfection of the irradiated and unirradiated (0001) cleaved surfaces of the crystals is studied using the bulk method of X-ray topography. The topographs supplement the findings suggestive of modifications in the crystalline quality of SrFe 12 O 19 on irradiation with SHI of Li 3 + . Etching of the (0001) cleaved surfaces in H 3 PO 4 at 120°C suggests that the dissolution characteristics of the surfaces get affected on irradiation with SHI of Li 3 + , besides supporting the findings of HRXRD and X-ray topography regarding modifications in the perfection of SrFe 12 O 19 on irradiation.

A quarter of a century after their discovery the mechanism that pairs carriers in the cuprate high-Tc superconductors (HTS) still remains uncertain. Despite this the general consensus is that it is probably magnetic in origin [1] so that the energy scale for the pairing boson is governed by J, the antiferromagnetic exchange interaction. Recent studies using resonant inelastic X-ray scattering strongly support these ideas [2]. Here as a further test we vary J (as measured by two-magnon Raman scattering) by more than 60 changing ion sizes in the model HTS system LnA2Cu3O7-δ where A=(Ba,Sr) and Ln=(La, Nd, Sm, Eu, Gd, Dy, Yb, Lu). Such changes are often referred to as "internal" pressure. Surprisingly, we find Tcmax anticorrelates with J where internal pressure is the implicit variable. This is the opposite to the effect of external pressure and suggests that J is not the dominant energy scale governing Tcmax.

ZnS(en)(0.5) complex (en=ethylenediamine) can be synthesized by solvothermal route as thin sheet-like crystals using en as the single solvent. We studied the influence of the main synthesis parameters (i.e. temperature, pressure, time, reactant type and concentration) on the compound crystallization kinetics to achieve control on shape and dimensions of the ZnS(en)(0.5) nanoplatelets. We achieved a significant reduction of the platelet dimensions, while maintaining acceptable yield, by using a single piece of metal zinc as the Zn2+ source. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Impedance spectroscopy measurements show that complex conductivity of thermally ablated CH3NH3SnCl3 films is strongly enhanced when humidity increases. Coplanar two-electrode test devices are modeled through an equivalent circuit comprising one resistance and two constant phase elements. It is shown that the influence of ambient humidity is mainly resistive. The dynamic responses of the devices to humidification/dehumidification cycles point out that the a.c. current varies by more than three orders of magnitude when humidity is varied between dry air and 80% relative humidity. The rise times are few hundred seconds while fall times are as short as few tens of seconds. This observation suggests that impedance variations are determined by mechanisms involving loosely bound water molecules physisorbed at the surface of the hybrid film. The results obtained are discussed in terms of protonic conduction.

Among the correlated electronic systems, BaVS3 which exhibits both itinerant and localized states as well as a subtle interplay betwen charge, orbital, spin and lattice degrees of freedom, is a model system. Its electronic structure consists in a broad quasi–one-dimensional (1D) dz2 band and two quasi-degenerate narrow e(t2g) bands. Pure BaVS3 exhibits a metal-insulator transition (MIT) driven by a Peierls instability in the dz2 band. We present a structural investigation showing that in chemically substituted Ba1- xSrxVS3 and in non-stoichiometric BaVS3- δ, the commensurate Peierls distortion of BaVS3 is replaced by an incommensurate modulation that we attribute to a charge ordering (CO) of the localized e(t2g) electrons. This unexpected structural feature is discussed in relationship with the concomitant drastic change of magnetic properties of the system.

Dielectric behaviour of flux grown substituted crystals bearing composition SrGaxInyFe12−(x+y)O19 (x=5, 7, 9; y=0.8, 1.3, 1.0) is reported. Variation of dielectric constant (ɛ/), dielectric loss (tanδ) and ac conductivity (σac) with temperature in the range 30–500°C under the frequency of the applied ac field in the range 1–104kHz for all the varied compositions are analyzed and explained. Swift heavy ion irradiation effects on these parameters are investigated. On irradiation the crystals show changes in the values of dielectric constant (ɛ/), dielectric loss (tanδ) and ac conductivity (σac). The frequency variation of ɛ/ and tanδ is explained by Koop's phenomenological theory and hopping frequency of electrons between Fe2+ and Fe3+ on octahedral sites for both irradiated and unirradiated crystals.

γ-CuCl microcrystals were found to segregate in self-assembled (CnH2n+1NH3)2CuCl4 hybrid organic-inorganic films deposited by single source thermal ablation. The microcrystals dispersed in the hybrid have sizes of 35 nm, as estimated from X-ray diffraction patterns. The UV photoluminescence efficiency of the embedded microcrystals is more than 100 times higher than that of CuCl films having similar crystallite sizes.

We describe the preparation, structural and transport properties of CH3NH3SnBr3 organic–inorganic hybrid films (500 nm thick), which crystallize as cubic perovskites. They were deposited by single source thermal ablation technique, in a 10-6 mbar vacuum chamber on glass, polymeric and crystalline substrates. X-ray diffraction proved that they were well crystallized and c-axis oriented.

Using vibrating sample magnetometery (VSM) 50MeV Li3+ ion irradiation effects on magnetic properties of single crystals of SrGaxInyFe12−(x+y)O19 (where x=0, 5, 7, 9; y=0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in strontium hexaferrite crystals decreases the value of magnetization sharply, which is attributed to shifting of collinear magnetic order to a non-collinear one. Reduction of magnetization is also explained to be as a result of the occupation of the crystallographic sites of Fe3+ by Ga3+ and In3+. The Li3+ ion irradiation decreases the value of magnetization, irrespective of whether the crystals are Ga–In substituted or unsubstituted crystals of SrFe12O19. The result is interpreted in terms of the occurrence of a paramagnetic doublet in crystals replacing magnetic sextuplet as a result of irradiation. Substitution of Ga–In in Strontium hexaferrite decreases the value of anisotropy constant. Irradiation with Li3+ ions increases the values of anisotropy field for both substituted as well as unsubstituted crystals. Substitution with Ga–In also decreases the Curie temperature (Tc) but the irradiation with Li3+ ions does not affect the curie temperature of either Ga–In substituted or pure SrFe12O19 crystals.

The semiconducting $\mathrm{Na}{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$ is a doping-free compound with several coexistent properties such as orbital ordering, charge ordering, and magnetic orderings of different types. We investigated its dielectric response by means of frequency impedance measurements in the range from $20\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. Standard measurements on metallized samples exhibit an apparent colossal dielectric constant (CDC) with an ${ϵ}_{R}$ value of several thousands at low frequencies, but a careful equivalent circuit analysis allows one to ascribe the observed CDC to the effect of a depletion layer on the metal-semiconductor junctions. We bypass this effect by means of a nonstandard technique employing mica linings: the resulting dielectric behavior exhibits the presence of the charge ordering transition at ${T}_{\mathit{CO}}=176\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and shows a net bulk dielectric constant value ${ϵ}_{R}\ensuremath{\simeq}68$ at room temperature.

To study the origin of the magnetic transition in BaVS3, we measured the dc magnetization on La0.1Ba0.9VS3 sintered samples near the ferromagnetic transition. Effective critical exponents and amplitudes are obtained by means of standard modified Arrot plots and the Kouvel-Fisher method, while asymptotic critical exponents and amplitudes are obtained by means of "correction to scaling" analysis. The two methods yield similar results, but the latter is superior with respect to the achieved uncertainty. The obtained results indicate that the universality class of magnetic interactions driving the transition changes from short to long range when cooling through T-c.

Similarly to the half-doped manganese oxides with perovskite structure like La 0.5 Ca 0.5 MnO 3 , the double perovskite compound NaMn 7 O 12 contains an equal number of Mn 3+ and Mn 4+ ions in the corner-sharing network of MnO 6 octahedra and exhibits a CE order of the charge and spins of these ions at low temperature. Though, in NaMn 7 O 12 the order is complete, the charge and spin ordering transitions are sharp and the system is free of disorder, phase coexistence or structural inhomogeneities thanks to the absence of chemical substitutions. Here we discuss two unusual features of the CE structure of NaMn 7 O 12 : (1) the e g 3 d x 2 − y 2 orbital ordering expected from the direct crystallographic observation of compressed Mn 3+ O 6 octahedra below the charge ordering transition; (2) the existence of a large amount of low-energy excitations evidenced by the low temperature behavior of the specific heat. We propose a picture of nearly degenerate spin and orbital configurations of the CE structure arising from the peculiar orbital ordering.

Vn-xTixO2n-l Magneli phases have been synthesized under vacuum in powder form (n=4, 0 <= x <= 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl4 and NH4Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 nun were obtained when in presence of NH4Cl or TeCl4, respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Vegard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V4O7. The metal-insulator transitions observed in V4O7 and V5O9, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Pure Strontium hexaferrite grown by flux method were used in present investigation. Dielectric analysis was carried out using fully automated HP4192A impedance analyzer. The samples were irradiated using Lithium beam of energy 50 MeV with fluence rate 1 × 1013 ions/cm2 at NSC, New Delhi. Dielectric studies of both irradiated and unirradiated samples have been carried out and the effect of irradiation is studied. The variation of dielectric constant ϵ′ for unirradiated and irradiated SrFe12O19 were studied as a function of frequency of a.c. field in the frequency range 1 KHz to 10 MHz from room temperature to 200°C. Dielectric constant is found to decrease with frequency, however, ϵ′ increases with temperature for both virgin as well as irradiated crystals. The crystals show increase in dielectric constant after irradiation. The variation of tanδ with frequency shows cusps for all samples. The variation has been explained on the basis of Maxwell-Wagner Interfacial polarization.