Arun Mahajan

Synthesis and characterization of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy)

A systematic investigation of layered perovskite oxides with general formula Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy) has been undertaken mainly to understand their structural, magnetic, as well as electrical behavior. The materials were prepared by the ceramic method. X-ray data have been analyzed by using program Checkcell and the variations of various parameters are explained. It has been concluded that not only A-site cation radius, , but also the size variance factor (σ2) influence electrical and magnetic properties. A systematic study of electrical resistivity of all the four materials was undertaken as a function of temperature to understand the conduction mechanism. On analyzing the electrical resistivity data, it has been concluded that variable range hopping model is found to fit well. The magnetic studies suggest that the phases are antiferromagnetic and this behavior could arise from Mn4+–O–Mn4+, and Fe3+–O–Fe3+ superexchange interaction.

Structure and magnetic properties of nano-sized perovskite oxide La0.5Sr0.5Ti0.5Fe0.4Cr0.1O3 synthesized by the citrate precursor method

A new nano-sized perovskite oxide La0.5Sr0.5Ti0.5Fe0.4Cr0.1O3 has been prepared according to the citrate precursor method at two different temperatures. Rietveld profile analysis shows that the phase crystallizes with the orthorhombic unit cell in the space group Pbnm. The size reduction due to the decrease in calcination temperature leads to an increase in lattice parameters and an expansion of the cell volume. The average grain size obtained from the TEM measurement is found to be larger than the observed crystal size obtained from XRD. The magnetic studies suggest that the anti-ferromagnetic interactions are dominant because of Fe3+–O–Fe3+ and Cr3+–O–Cr3+ exchange interactions.Graphical Abstract

Zinc phthalocyanine nanowires based flexible sensor for room temperature Cl2 detection

We have fabricated highly sensitive and Cl2 selective flexible sensor by depositing solution processed zinc phthalocyanine nanowires onto the flexible PET substrate and studied its Cl2 sensing characteristics in Cl2 concentration range 5-1500 ppb. The flexible sensor has a minimum detection limit as low as 5 ppb of Cl2 and response as high as 550% within 10 seconds. Interestingly, the sensor exhibited enhanced and faster response kinetics under bending conditions. The gas sensing mechanism of sensor has been discussed on the basis of XPS and Raman spectroscopic studies which revealed that zinc ions were the preferred sites for Cl2 interactions.We have fabricated highly sensitive and Cl2 selective flexible sensor by depositing solution processed zinc phthalocyanine nanowires onto the flexible PET substrate and studied its Cl2 sensing characteristics in Cl2 concentration range 5-1500 ppb. The flexible sensor has a minimum detection limit as low as 5 ppb of Cl2 and response as high as 550% within 10 seconds. Interestingly, the sensor exhibited enhanced and faster response kinetics under bending conditions. The gas sensing mechanism of sensor has been discussed on the basis of XPS and Raman spectroscopic studies which revealed that zinc ions were the preferred sites for Cl2 interactions.

Synthesis and characterization of half-doped chromium manganite La0.3Dy0.2Sr0.5Mn0.5Cr0.5O3

The half-doped chromium manganite La0.3Dy0.2Sr0.5Mn0.5Cr0.5O3 has been studied by X-ray diffraction and magnetic and transport measurements. The sample was found to be single phase and crystallized with orthorhombic structure in the space group Pnma. Magnetic measurements showed that the ferromagnetic interactions are dominant and the phase follows Curie–Weiss law only in the high-temperature region. The sample is semiconducting and the transport properties are dominated by the adiabatic small polaron hopping mechanism.Graphical abstract

Synthesis, structure, and magnetic properties of the perovskite La0.3Sm0.2Sr0.5Ti0.5Fe0.5O3

Perovskite oxide La0.3Sm0.2Sr0.5Ti0.5Fe0.5O3 has been synthesized by a citrate-gel precursor method. The Rietveld analysis of the XRD data showed that the sample crystallizes with a orthorhombic structure in the space group Pbnm. Magnetic properties suggest that antiferromagnetic interactions are dominant due to Fe3+–O–Fe3+ units.Graphical abstract

Synthesis, structure, and magnetic properties of the perovskite La 0.3 Sm 0.2 Sr 0.5 Ti 0.5 Fe 0.5 O 3

Perovskite oxide La0.3Sm0.2Sr0.5Ti0.5Fe0.5O3 has been synthesized by a citrate-gel precursor method. The Rietveld analysis of the XRD data showed that the sample crystallizes with a orthorhombic structure in the space group Pbnm. Magnetic properties suggest that antiferromagnetic interactions are dominant due to Fe3+–O–Fe3+ units.Graphical abstract

Rietveld Refinements of K 2 NiF 4 -Type Phases Ln 0.5 Sr 1.5 Mn 0.5 Fe 0.5 O 4 (Ln = La, Nd, Gd, and Dy)

Transition metal oxides of composition A2BO4 (A is usually a rare-earth, alkaline-earth, or alkali ion and B can be a 3d or 4d transition-metal ion) with the layered K2NiF4 structure type have long been studied because they display a variety of unusual structural and magnetic properties. They have received considerable interest in recent years, particularly since the discovery of superconductivity in La2−xBaxCuO4 and Sr2RuO4.1−3 The two dimensional A2BO4 consists of perovskite-like corner linked BO6 sheets interleaved by the rock-salt AO layers, in which the large A cations are arranged in the plane formed by O atoms at the top (or bottom) of the octahedral with nine nearest O neighbors. One important factor that determines the structure of the A2BO4 compounds is the matching between the perovskite-like BO6 layers and the A-type cations. A measure of the bond length matching can be calculated from a version of the Goldschmidt tolerance factor t = (rA + rO)/ √2(rB + rO) for perovskite and perovskite-derived structure; ideal matching between the A cation and one layer of linked BO6 octahedra occurs for t ≈1 and the structure formed is tetragonal described in the space group I4/mmm (no. 139). In our earlier work, we have reported the synthesis, electric transport and magnetic properties of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy). In this reported work, much has been left about the structural characterization of the phases. In the present work, we report structural characterization of the Ln0.5Sr1.5Mn0.5Fe0.5O4 phases (Ln = La, Nd, Gd, and Dy) by Rietveld analysis using GSAS program. The bond angles and bond distances have been determined on the basis of structural parameters derived from structural refinements. EXPERIMENTAL

Rietveld Refinements of K2NiF4-Type Phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy)

Transition metal oxides of composition A2BO4 (A is usually a rare-earth, alkaline-earth, or alkali ion and B can be a 3d or 4d transition-metal ion) with the layered K2NiF4 structure type have long been studied because they display a variety of unusual structural and magnetic properties. They have received considerable interest in recent years, particularly since the discovery of superconductivity in La2−xBaxCuO4 and Sr2RuO4.1−3 The two dimensional A2BO4 consists of perovskite-like corner linked BO6 sheets interleaved by the rock-salt AO layers, in which the large A cations are arranged in the plane formed by O atoms at the top (or bottom) of the octahedral with nine nearest O neighbors. One important factor that determines the structure of the A2BO4 compounds is the matching between the perovskite-like BO6 layers and the A-type cations. A measure of the bond length matching can be calculated from a version of the Goldschmidt tolerance factor t = (rA + rO)/ √2(rB + rO) for perovskite and perovskite-derived structure; ideal matching between the A cation and one layer of linked BO6 octahedra occurs for t ≈1 and the structure formed is tetragonal described in the space group I4/mmm (no. 139). In our earlier work, we have reported the synthesis, electric transport and magnetic properties of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy). In this reported work, much has been left about the structural characterization of the phases. In the present work, we report structural characterization of the Ln0.5Sr1.5Mn0.5Fe0.5O4 phases (Ln = La, Nd, Gd, and Dy) by Rietveld analysis using GSAS program. The bond angles and bond distances have been determined on the basis of structural parameters derived from structural refinements. EXPERIMENTAL

Rietveld Refinements of K 2 NiF 4 -Type Phases Ln 0.5 Sr 1.5 Mn 0.5 Fe 0.5 O 4 (Ln

Transition metal oxides of composition A2BO4 (A is usually a rare-earth, alkaline-earth, or alkali ion and B can be a 3d or 4d transition-metal ion) with the layered K2NiF4 structure type have long been studied because they display a variety of unusual structural and magnetic properties. They have received considerable interest in recent years, particularly since the discovery of superconductivity in La2−xBaxCuO4 and Sr2RuO4.1−3 The two dimensional A2BO4 consists of perovskite-like corner linked BO6 sheets interleaved by the rock-salt AO layers, in which the large A cations are arranged in the plane formed by O atoms at the top (or bottom) of the octahedral with nine nearest O neighbors. One important factor that determines the structure of the A2BO4 compounds is the matching between the perovskite-like BO6 layers and the A-type cations. A measure of the bond length matching can be calculated from a version of the Goldschmidt tolerance factor t = (rA + rO)/ √2(rB + rO) for perovskite and perovskite-derived structure; ideal matching between the A cation and one layer of linked BO6 octahedra occurs for t ≈1 and the structure formed is tetragonal described in the space group I4/mmm (no. 139). In our earlier work, we have reported the synthesis, electric transport and magnetic properties of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy). In this reported work, much has been left about the structural characterization of the phases. In the present work, we report structural characterization of the Ln0.5Sr1.5Mn0.5Fe0.5O4 phases (Ln = La, Nd, Gd, and Dy) by Rietveld analysis using GSAS program. The bond angles and bond distances have been determined on the basis of structural parameters derived from structural refinements. EXPERIMENTAL

Synthesis, magnetic and electric transport properties of mixed-valence manganites La{sub 0.5+x}Sr{sub 1.5−x}Mn{sub 0.5}Cr{sub 0.5}O{sub 4} (x=0.1, 0.2 and 0.3)

Abstract A series of mixed-valence manganites La0.5+xSr1.5−xMn0.5Cr0.5O4 were synthesized by sol–gel method. Rietveld profile analysis shows that the phases crystallize with tetragonal unit cell in the space group I4/mmm. The lattice parameter c increases with increase in x while a parameter almost remains constant. The Weiss constant (θ) is positive for all the phases and found to increase with increase in x. The ferromagnetic interactions becomes more dominant with increase in x due to increase in Mn3+–O–Mn4+ and Mn3+–O–Cr3+ double exchange interactions. Resistivity can be described by the polaron hopping and the variable range hopping model. It was found that the transport mechanism is dominated by Motts variable range hopping (VRH) model with a decrease of Mott localization energy with increase in x, which explains the decrease of resistivity.