Raman studies of rod-like bismuth strontium manganites (original) (raw)
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Studies on rod shaped bismuth strontium manganite ceramics
Rods of Bi 1−x Sr x MnO 3 (BSM) (0.20 ≤ x ≤ 0.50) having different dimensions were synthesized by the solid state reaction method. The replacement of bismuth by strontium in BSM plays an important role in changing the cell volume, and DC resistivity. The surface morphology varied with strontium content and changes from cubic to rods of different sizes. The room temperature resistivity of BSM decreases with strontium from 0.21 M cm to 0.11 M cm. These manganites follow the Arrhenius equation. The thermistor constant increases with Sr content from ∼ 793 K to 1735 K, the maximum being for x = 0 20 and minimum for x = 0 50.
Structural mechanical properties of Sr doped Bismuth manganites
Bismuth strontium manganites Bi 1 -x Sr x MnO 3 (0.20 ≤ x ≤ 0.50) belonging to the orthorhombic structural family were prepared in furnace using a solid state reaction technique. Thick films of Bi (1 -x) Sr x MnO 3 were prepared by simple screen printing route. X ray diffraction data suggest that the synthesized materials have an orthorhombic structure. For synthesized materials, texture coefficient (TC), dislocation density (ρ D ), density of crystallites per unit area (ψ), and mechanical properties are reported along with the influence of x on the structure and mechanical properties of BiMnO 3 thick films.
Microwave Studies of Bismuth Strontium Manganite Thick-Films by Superstate Method
We report structural and microwave properties of rod shaped bismuth strontium manganite , thick-films prepared by screen printing method. The orthorhombic phase formation was confirmed by XRD. The micro rods like morphology and grain size were observed by using SEM analysis. Modification in microstripline properties like microwave absorption , transmittance, and effective dielectric constant which is being done by simple superstrate Bi 1−x Sr x MnO 3 (BSM) thick-films at very high frequencies (microwaves). The effective dielectric constant is due to superstrate, which lies in between 10.41 to 29.22 for thick films.
A Bismuth Manganite with the “2212” Structure: Bi2−xPbxSr1.5Ca1.5Mn2O9−δ
Journal of Solid State Chemistry, 1997
A manganite Bi 2؊x Pb x Sr 1.5 Ca 1.5 Mn 2 O 9؊ , with the 2212 structure, has been synthesized for the first time. Its structural study by powder X-ray diffraction and by electron microscopy has been performed for two compositions, x ؍ 0.5 and x ؍ 1. The average structure consists of double perovskite layers (P) involving MnO 6 octahedra and MnO 5 pyramids intergrown with distorted triple rock salt layers (RS). The perovskite cages are mainly occupied by strontium so that these phases can be formulated [Bi 2؊x Pb x Ca 1.33 Sr 0.67 ] RS [Sr 0.83 Ca 0.17 ] P Mn 2 O 9؊. The HREM investigation shows that the composition x ؍ 0.5 exhibits an incommensurate modulated structure similar to that observed for the superconducting bismuth cuprate and for the iron-based 2212 compound. In contrast, the composition x ؍ 1 does not exhibit any modulation. Although they are rare, some extended defects are observed especially for BiPbSr 1.5 Ca 1.5 Mn 2 O 9؊. Both oxides are semiconductors.
Ferroelectrics, 2003
Raman spectra and pyroelectric studies in bismuth doped SrTiO 3 ceramics, with general formulae Sr (1−1.5x) Bi x TiO 3 , were undertaken. For x = 0.0053, the low frequency Raman spectra exhibit striking similarities with the spectra of the undoped ceramics also revealing the existence of a polar soft-mode TO 1 , that obeys the classical Cochran softening law. The sample with x = 0.133 presents a very different dynamics, and its Raman spectra give evidence for the inexistence of an anti-ferrodistorsive phase transition, that occurs in the undoped ceramics at 104 K. Pyroelectric measurements disclose the existence of small electrical dipoles probably due to polar grain boundaries, off-centre positions of Bi 3+ and Ti 4+ ions, and Sr vacancies, that strongly influence the behaviour of these systems with temperature variation. There is a strong evidence for the existence of a relaxor state in the x = 0.133 ceramic at low temperatures. Keywords: Ferroelectric relaxor; quantum paraelectricity; Raman spectra; pyroelectric current [405]/49 50/[406] A. ALMEIDA et al.
Multiferroic bismuth manganite prepared by mechanochemical synthesis
Journal of the European Ceramic Society, 2010
Multiferroic bismuth manganite (BiMnO 3) is known as a material that exhibits both ferromagnetic and ferroelectric properties making it interesting for various technological applications. Unfortunately, preparation of BiMnO 3 is not possible by a conventional solid-state reaction and it can form only from mixture of oxides at high pressures (>40 kbar). In this work single-phased BiMnO 3 was prepared for the first time by mechanochemical synthesis in a planetary ball mill. A mixture of Bi 2 O 3 and Mn 2 O 3 was intensively milled in air atmosphere, using stainless steel vials and balls. According to analysis of XPRD results BiMnO 3 obtained after milling for 240 min has a tetragonal structure with lattice parameters a = 3.9230 Å, c = 3.920 Å and a crystallite size of 16.8 nm. The cumulative energy introduced into the system during milling for 240 min was 401 kJ/g. It was found that the obtained powders were agglomerated. Corresponding agglomeration factors were calculated from the results of BET and particle size distribution analysis.
J Solid State Chem, 1998
A manganite with a ''tubular'' structure derived from the 2201-type, Bi 3.6 Sr 12.4 Mn 8 O 28؉ , has been synthesized. Its complex crystal chemistry has been studied using XRD, ND, and HREM techniques. It crystallizes in an orthorhombic cell, space group Pbnb, with a ؍ 5.4946 A s , b ؍ 23.595(1) A s , and c ؍ 23.580(1) A s. This structure can be described as an intergrowth, along b, of two types of (010) slices: ''2201''-type slices [Bi 2 Sr 2 MnO 6 ] that are two octahedra thick and manganesedeficient perovskite-related slices [Sr 8 Mn 6 O 16؉ ] that are one octahedron thick. A similar stacking is observed along c, which endows the structure with a pseudotetragonal character. Another way to describe this structure is to consider criss-crossing layers of manganese polyhedra forming tubes, where the [BiO] rows are inserted, and oxygen-deficient pillars, built up of four Mn polyhedra. This phase represents the n ؍ 2 member of a new ''tubular'' family [Bi 2 Sr 2 MnO 6 ] n [Sr 8 Mn 6 O 16؉ ]. Intergrowth and shearing mechanisms arise along the b and c directions, in agreement with the pseudotetragonal character of the structure. The investigation of the transport and magnetic properties of this new manganite shows that it is an insulator and exhibits weak antiferromagnetism at low temperature (p ؍ ؊650 K); the high-temperature data evidence an effective magnetic moment of 4.7 B characteristic of high-spin Mn 3؉ (th ؍ 4.9 B).
Bismuth strontium manganites (BSM) with variation in strontium content have been synthesized by simple solid state reaction method. X-ray diffraction data show that the samples have orthorhombic structure with crystallite size ~40 to 60 nm. SEM studies reveal morphology of micro-rods and micro-flakes. The dielectric constant (ε') and the dielectric loss (tan δ) decreases with the strontium content and the applied frequency which has been attributed to Maxwell-Wagner polarization. The microwave conductivity of samples decreases from 8.9 S/cm to 2.29 S/cm at 8.2 GHz as strontium increases. The penetration depth has also been reported at microwave frequencies from 8 -18 GHz.
Journal of Nanoparticle Research
We have studied the formation of BiMnO3 (BMO) nanocrystalline perovskite powder produced by high-energy milling of the constituent oxides. The crystal structure and the amount of crystalline and amorphous phases in the powder as a function of the milling time were determined with XRPD using Rietveld refinement. BMO perovskite formed directly from highly activated nano-sized constituent oxides after 240 min of milling and subsequently grew during prolonged milling. The morphology, structure, and chemical composition of the powder were investigated by SEM and TEM. A clear ferromagnetic transition was observed at T C ~66 K for a sample milled for 240 min and increased with milling time. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. The magnetic properties of the obtained BMO powders were found to change as a function of milling time in a manner consistent with variations in the nanocomposite microstructure.