We report the synthesis, (micro)structural, magneto-transport and magnetization of polycrystalline La 2/3 Ca 1/3 MnO 3 :Ag x composites with x = 0.0, 0.1, 0.2, 0.3 and 0.4. The temperature coefficient of resistance (TCR) near ferromagnetic (FM) transition is increased significantly with addition of Ag. The FM transition temperature (T FM ) is also increased slightly with Ag addition. Magneto-transport measurements revealed that magneto-resistance MR is found to be maximum near T FM . Further the increased MR of up to 60% is seen above 300 K for higher silver added samples in an applied field of 7 Tesla. Sharp TCR is seen near T FM with highest value of up to 15 % for Ag (0.4) sample, which is an order of magnitude higher than as for present pristine sample and best value yet reported for any polycrystalline LCMO compound. Increased TCR, T FM and significant above room temperature MR of La 2/3 Ca 1/3 MnO 3 :Ag x composites is explained on the basis of improved grains size and connectivity with silver addition in the matrix. Better coupled FM domains and nearly conducting grain boundaries give rise to improved physical properties of the La 2/3 Ca 1/3 MnO 3 manganites. Ag composites Ag is not substituted into main LCMO lattice but remain rather as an additive in the system. (280 K) is comparable to aligned thin films [6,8,15] of LCMO, and to our knowledge is the best one yet obtained for any polycrystalline mangenites. As far fixed temperature and varying field MR is concerned its shape is changed from U type to V type. And is maximum at all fields up to 7 Tesla at 300 K. Infact with an increase in Ag content the low T below 300K MR% decrease and the room temperature 300 K increase. For LCMO: Ag (0.4) sample the MR of up to 60% is observed in 7 Tesla field at 300 K. Even at low fields of say 1 Tesla the MR of up to 16% is seen.The results of magnetization and magneto transport of LCMO:Ag x composites can be summarized as follows: 7 1. Ag does not substitute into host LCMO matrix in our polycrystalline LCMO:Ag x composites but improved significantly the grain morphology of the host.2. The T MI and T c remain nearly invariant with increase in x (Ag content).3. The sharpness of insulator-metal transition increases dramatically with increase in x (Ag content) and high (15%) sharp TCR is observed for Ag composites 4. Though the MR is seen in all the samples right from 300 K down to 5 K, the same is negligible at 300 K and more at lower T for pure sample and is maximum at 300 K and least at 5 K for Ag (0.4) containing compounds. DISCUSSIONNow we try to explain in broad sense the main results summarized above, as far as (1) is concerned there are some very recent reports in literature, which deals with the LCMO and LCMO/ZrO 2 [20]. In all these composites the quality of the LCMO was deteriorated. In case of LCMO:Ag there is a good probability of Ag being distributed at grain boundaries and hence providing better connectivity of grains, which is seen in Fig. 2(b). In most of other composites [16][17][18][19][20] the addi...

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In this work, nanocrystalline MgO particles were prepared through combustion method using magnesium nitrate as oxidizer and hexamine as a fuel. The materials obtained by combustion method were subsequently annealed at 800 ∘ C for 3 h to improve the crystallinity and phase purity. The obtained MgO nanomaterials were characterized by powder X-ray diffraction analysis (XRD), infrared (IR) spectroscopy, photoluminescence (PL), near-infrared (NIR) spectroscopy, and scanning electron microscopy (SEM). The cubic crystal structure with lattice parameter, a = 0.4210(4) nm with average crystalline size of 22 nm, is obtained for the nano-MgO particles. The PL emission spectrum of nanocrystalline MgO materials exhibits three emission peaks at 432, 465, and 495 nm which are due to various structural defects. The SEM results expose the fact that the MgO nanomaterials are seemingly porous and highly agglomerated with fine particles. Owing to the higher reflectance of prepared nanocrystalline MgO, it can be used as NIR reflective pigments. The present results prove that the combustion technique using hexamine can produce the materials with high crystallinity. To the best of our knowledge, this is the first report on the synthesis of nanocrystalline MgO materials by combustion method using hexamine as a fuel.

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The mechanical and superconducting properties of MgB 2 wires heat treated at various conditions have been investigated. Superconducting MgB 2 wires, fabricated by the powder-in-tube (PIT) method, show a transition temperature T c at 32.4 K for the as-rolled wire as shown by dc-resistivity measurement. It is found that the T c is improved (37.3-38.4 K) by subsequent Ar annealing treatment under various sintering temperatures and times. Remarkably, the annealed samples show significant improvement in the overall quality of the samples. On annealing at 1323 K for 0.6 ks, we obtained the best quality sample with a J c of 470 A mm −2 at 2.0 T. In order to find out the irreversible field (B irr ), the technique of the Kramer plot was applied. The B irr obtained was 7.6 and 9.6 T, for the as-rolled as well as the annealed samples at 1073 K for 3.6 ks, respectively. The mechanical properties were measured under tensile load. The yield stress was 450 MPa for the as-rolled sample and decreased by annealing at 1323 K for 0.6 ks to 110 MPa. After the wires were heat treated at temperatures between 1073 and 1323 K and tensile-stressed up to their yield stress at room temperature. The critical current measurements were carried on such samples at 4.2 K under applied magnetic fields of 2 and 5 T. The stress level for the 95% tolerance of critical current was determined to 97 MPa.