Ram Niwas Singh

Colossal magnetoresistance in epitaxial La(1−x−y)NayMnO3 thin film

We have synthesized La0.83Na0.11MnO2.93 by heating La2O3 and MnCO3 in NaCl melt at 900 °C. The exact composition was arrived by analyzing each ion by an independent chemical method. The compound crystallized in a rhombohedral structure and showed an insulator-to-metal transition at 290 K. Epitaxial thin films were fabricated on LaAlO3 (100) using a pulsed laser deposition technique. The film also showed an insulator-to-metal transition at 290 K. Magnetoresistance [ΔR/R0=(RH−R0)/R0] was −71% near the insulator-to-metal transition temperature of 290 K at 6 T magnetic field.

Room temperature synthesis of metal fluorides and pyridinium fluorometallate complexes by the direct reaction of metals with pyridinium poly(hydrogen fluoride)

Metal powders (Pb, Cu, Zn, Mn, Al, Fe, Sn, Cr) are found to react directly with pyridinium poly(hydrogen fluoride) (PPHF) at room temperature to form metal fluorides/pyridinium fluorometallates and hydrogen. The reaction rate is dependent on the particle size of the metals and stirring conditions

Synthesis and studies on pyridinium pentafluorozirconate and pyridinium oxotetrafluoroniobate

Abstract Pyridinium pentafluorozirconate, (C5H5NH)ZrF5, and pyridinium oxotetrafluoroniobate, (C5H5NH)NbOF4, have been synthesised by the reaction of pyridinium poly(hydrogen fluoride), PPHF, with ZrOCl2 and Nb2O5, respectively. These new complexes have been characterised by chemical analysis, thermal analysis, X-ray diffraction and infrared spectra.

Pyridinidm Hexafluorotitanate and its Derivatives

Pyridinium hexafluorotitanate, (C5H5NH)(2)TiF6, has been prepared by the reaction of titanium metal with pyridinium poly(hydrogen fluoride), PPHF, at room temperature. Making use of (C5H5NH)(2)TiF6 as a precursor, ammonium and alkali metal hexafluorotitanates, M(2)TiF(6) (M = NH4, Na, K, Rb and Cs) have been synthesized by metathesis. These hexafluorotitanates have been characterized by chemical analyses, infrared and NMR (H-1 and F-19) spectroscopy and powder X-ray diffraction methods. Indexed powder X-ray diffraction data for Rb2TiF6 and Cs2TiF6 have been reported.

A study of the synthesis of Group I and Group II metal fluorides with pyridinium poly(hydrogen fluoride), PPHF

Abstract Alkali and alkaline earth metal fluorides, hydrogen fluorides and complex fluorides have been prepared by the reaction of the corresponding metal chloride, oxide and carbonate with pyridinium poly(hydrogen fluoride) at room temperature. The resulting compounds have been characterized by chemical analysis, IR and NMR ( 1 H, 13 C, 19 F) spectroscopy and XRD methods. The interesting feature is the formation of normal fluorides by lithium, calcium and magnesium, while sodium, potassium, rubidium, caesium, strontium and barium form fluoride complexes with HF, and beryllium gives rise to a pyridinium tetrafluoroberyllate salt. This salt has been synthesized and characterized for the first time.

STUDY OF THE REACTIONS OF PYRIDINIUM POLY(HYDROGEN FLUORIDE) WITH SOME TERNARY OXIDES

Abstract The products of the reaction of pyridinium poly(hydrogen fluoride), PPHF, with KIO 3 , Na 2 SnO 3 , NaBiO 3 , K 2 CrO 4 , Na 2 MoO 4 and Na 2 WO 4 were KIO 2 F 2 ; Na 2 SnF 6 ; NaHF 2 , BiF 3 ; K 3 CrF 6 , KHF 2 , (PyH) 3 CrF 6 ; NaHF 2 , (PyH) 2 MoO 2 F 4 ·2NaHF 2 ; and (PyH) 2 WO 2 F 4 ·2NaHF 2 , respectively, while KClO 3 , KBrO 3 and KIO 4 react with complete decomposition to form KHF 2 as the fluorinated product. This differential reactivity and mode of reaction has been discussed in terms of the oxidation state of the central atom, the nature and strength of the bonds and the complex behaviour of the formed intermediate or fluorinated products that undergo complexation or solvation with pyridine and/or hydrogen fluoride.

Synthesis and studies on pyridinium chlorofluoro complexes of indium and bismuth

Abstract Pyridinium trichlorotrifluoroindate, (C 5 H 5 NH) 3 InCl 3 F 3 , and pyridinium trichlorofluorobismuthate, C 5 H 5 NHBiCl 3 F, have been synthesised by the reaction of pyridinium poly (hydrogen fluoride), PPHF, with InCl 3 and BiCl 3 , respectively. These new complexes have been characterised by chemical and thermal analysis, NMR ( 1 H and 19 F) and infrared spectroscopy, and powder X-ray diffraction methods.

A study of the reaction of divalent transition metal chlorides with pyridinium poly(hydrogen fluoride), ppht, and the effect of potassium hydrogen fluoride on fluorination and complexation

Studies of the reaction of metal chlorides, MCl2 (M = Mn, Co, Ni, Cu, Zn) with PPHF at room temperature have shown that Mn, Co and Zn form the corresponding metal fluorides, MF2, while Ni and Cu form their dipyridine metal(II) dichloride complexes. Nickel and copper complexes further undergo fluorination and complexation by potassium hydrogen fluoride in PPHF to form KNiF3 and KCuF3.

Studies on Pyridinium Hexafluorostannate and Its Derivatives

Pyridinium hexafluorostannate, (C5H5NH)2SnF6, has been prepared by the reaction of stannous chloride or tin metal with pyridinium poly(hydrogen fluoride), PPHF, and identified by chemical analysis, IR and NMR (H-1, F-19, C-13). Making use of (C5H5NH)2SnF6 as a precursor, the following important hexafluorostannate salts have been synthesized in high yields at room temperature by ionic exchange: M2SnF6 (M = NH4, Na, K, Rb, Cs) and BaSnF6. These salts have been characterised by chemical analysis and infrared spectroscopy. Indexed powder X-ray diffraction data for Na2SnF6, Rb2SnF6 and Cs2SnF6 have been reported.

Syntheses and studies on pyridinium pxofluorocomplexes of molybdenum, tungsten andiodine

(C5H5NH)2MO2F4 (M = Mo and W) and C5H5NHIO2F2 have been synthesized at room temperature by the reaction of molybdic, tungstic or iodic acid, respectively, with pyridinium poly(hydrogen fluoride). These complexes have been characterized by chemical analyses, H-1 nmr and infrared spectroscopy.