Publications

Non-equilibrium magnetic properteis of single crystalline La0.7Ca0.3CoO3

Magnetic and electric properties of a single crystal of La0.7Ca0.3CoO3 have been experimentally studied. The system attains a ferromagnetic spontaneous moment below 170 K and exhibits a re-entrant spin-glass phase below 100 K. In the ordered and the re-entrant phases, the low field magnetic properties are strongly direction dependent, showing considerably higher magnetization values perpendicular than parallel to the c-axis. Magnetic relaxation experiments show that both the ferromagnetic and the re-entrant spin-glass phases are non-equilibrium states, where the system exhibits magnetic aging characteristic of spin-glasses and disordered and frustrated ferromagnets. *for correspondence: cnrrao@jncasr.ac.in

Melting of ionic solids and the born treatment

Melting temperatures of alkali halides have been calculated assuming that different structures of an ionic solid exhibiting polymorphism will have nearly identical energy around the melting point: the calculated value for CsCl shows good agreement with the observed value.

Synthesis and characterization of layered bismuth vanadates

Oxyanion derivatives of cuprate superconductors: Superconducting thallium cuprate oxysulfate, Tl0.5Pb0.5Sr4Cu2(SO4)Oy

A superconducting thallium cuprate oxysulfate of the composition Tl0.5Pb0.5Sr4Cu2(SO4)Oy, ( P4/mmm, a = 3.85 A ̊ , c = 16.6 A ̊ ) related to the 1223 type cuprate family has been characterized. Infrared spectra show that the sulfate ion is present as a bidentate ligand as expected from the structure.

Preface

No abstract is provided for this article.

Chemical synthesis of solid inorganic materials

Dynamics of charge transfer in the excited amine complexes of the fullerenes C60 and C70.

In benzene solution, C60 and C70 interact weakly in the ground state with amines having favourable oxidation potentials. Picosecond time-resolved absorption measurements show that on photoexcilation, the weak complexes undergo charge separation to produce ion pairs which in turn undergo fast geminate recombination either to produce the triplet state of the fullerenes or give back the ground slate of the complex, depending on the oxidation potential of the amine. Free-ion yield is generally negligible.

CCDC 283063: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A systematic study of four series of electron-doped rare earth manganates, Ln_<i>x</i>Ca_{1 <i>x</i>}MnO₃(Ln La, Nd, Gd and Y) over the<i>x</i> 0.02 0.25 composition range

Electrical and magnetic properties of four series of manganates Ln x Ca 1-x MnO 3 (Ln=La, Nd, Gd and Y) have been studied in the electron doped regime (x=0.02-0.25) in order to investigate the various inter-dependent phenomena such as ferromagnetism, phase separation and charge ordering.The general behavior of all the four series of manganates is similar, with some of the properties showing dependence on the average radius of the A-site cations, <r A > and cation size disorder.Thus, all the compositions show increase in magnetization at 100-120 K (T M ) for x<x max , the magnetization increasing with increasing x.The value of x max increases with decreasing <r A >, probably due to the increased phase separation induced by site disorder.This is also reflected in the larger width of the hysteresis loops at T<T M for small x or <r A >.In this regime, the electrical resistivity decreases with increasing x, but remains low and nearly constant T>T M .The percolative nature of the conduction mechanism at T<T M is substantiated by the fit of the conductivity data to the scaling law, σ ∝ |x c -x| p where p is in the 2-4 range.When x>x max , the materials become antiferromagnetic and charge-ordered at a temperature T CA , accompanied by a marked increase in resistivity.The value of T CA increases with increase in <r A > and x (upto x=0.3).Thus, all the four series of manganates are characterized by a phase-separated regime between x=0.02 and 0.1-0.15 and an antiferromagnetic charge-ordered regime at x>0.1-0.15.

<font>B</font>–<font>C</font>–<font>N</font>, <font>C</font>–<font>N</font> and <font>B</font>–<font>N</font> nanotubes produced by the pyrolysis of precursor molecules over <font>Co</font> catalysts

No abstract is provided for this article.

Magnetic Structure and Giant Magnetoresistance of Ferromagnetic La1−δMn1−δO3—An Example of Double-Exchange Striction?

A neutron powder diffraction study of the structure of the rhombohedral phase of La1−δMn1−δO3(δ = 0.04) as a function of temperature has been carried out. The crystal structure is well described at all temperatures by a model inR− 3c(a= 5.52264(5) andc= 13.3309(5) at 300 K) and the low temperature data contain magnetic contributions to the Bragg scattering due to ferromagnetic ordering belowT c∼ 200 K. The spin is canted at approximately 45° from [001]. The Mn–O–Mn angle decreases on cooling toT c, but shows a slight increase on further cooling, presumably due to the onset of a double-exchange striction effect. Resistivity and magnetization data corroborate the neutron findings and reveal an insulator to metal transition close toT cwith a negative giant magnetoresistance value of ∼50% at this temperature. The results confirm the striking similarity between the structural, magnetic, and conducting properties of rhombohedral La1−δMn1−δO3and those of the solid solution La1−x A x MnO3(x∼ 0.3).

Dependence of the Reactivity of <font>Ag</font> and <font>Ni</font> Clusters Deposited on Solid Substrates on the Cluster Size

Phase transitions

Many solids undergo transformations from one crystal structure to another as the temperature or pressure is varied and this phenomenon is popularly referred to as polymorphism. Whereas polymorphism normally refers to phase transitions involving changes in the atomic configurations in crystals, there are also transitions where the electronic or spin configuration undergoes changes. The subject of phase transitions is not only of great academic interest but also of technological importance. Phase transitions are exhibited by a wide variety of systems (Table 4.1) from simple metals and alloys to complex inorganic and organic materials. The subject has grown enormously in the last two decades with new types of transitions as well as new approaches to explain the phenomena. Traditionally, the subject has been of vital concern to metallurgists (Porter & Easterling, 1981) but there are many aspects of great importance to solid state chemistry (Rao, 1984). Varied aspects of phase transitions such as critical phenomena, soft modes, mechanisms and changes in properties at phase transitions have been treated in a unified manner by Rao & Rao (1978). We shall deal with some highlights of the subject and examine some classes of transitions in this chapter.

Decoration of Few-Layer Graphene-Like MoS2 and MoSe2 by Noble Metal Nanoparticles

No abstract is provided for this article.

The First Organically Templated Open‐Framework Metal Selenate with a Three‐Dimensional Architecture.

For Abstract see ChemInform Abstract in Full Text.

Normal vibrations of cyclic tetraglycine

Normal vibration analysis of cyclic tetraglycine has been carried out employing the Urey‐Bradley force field and the vibrational assignments are compared with those in related molecules.

Aufbau Principle of Complex Open-Framework Structures of Metal Phosphates with Different Dimensionalities

No abstract is provided for this article.

AN INSITU EXAFS INVESTIGATION OF BIMETALLIC CU-NI/GAMMA-AL2O3 CATALYSTS