Solid State Phenomena Vol. 317

Abstract: Colossal magnetoresistive (CMR) materials have huge potential in modern application and it has been widely used in magnetic sensing industry. From the literature, an incorporation of secondary insulating phase into mixed-valence manganites could improve its extrinsic effect especially low-field magnetoresistance (LFMR). However, nanoparticle addition could lead to substitution and diffusion with its parent compound. In this work, the structural and electrical properties of La_0.7Ca_0.3MnO₃ (LCMO) were investigated by adding the α-Fe₂O₃ nanoparticle with ratio of 0.00, 0.05, 0.10, 0.15 and 0.20 as the artificial grain boundaries. The LCMO compound has been synthesised using sol-gel route. The samples were chosen to sinter at 800°C to obtain the pure LCMO phase by referring to the thermogravimetric analysis (TGA). The structural properties were investigated by an X-ray diffractometer (XRD) while electrical properties were measured by a four-point probe (4PP) system. XRD patterns showed the coexistence of two phases (LCMO & α-Fe₂O₃). LCMO crystallised in orthorhombic structure with space group Pnma while α-Fe₂O₃ exhibited in hexagonal form with space group R-3c. As the content of α-Fe₂O₃ increases, the resistivity of the samples increases drastically. Nevertheless, the addition of iron oxide has no significant effect on the metal-insulator transition temperature (T­_MI). From the XRD and 4PP analysis, it can be deduced that the α-Fe₂O₃ nanoparticles do not react with LCMO compound and successfully formed the La_0.7Ca_0.3MnO₃ /α-Fe₂O₃ composites. The resistivity increases when the nano-sized α-Fe₂O₃ is added into LCMO nanocomposites due to the insulator nature of α-Fe₂O₃.

Abstract: In this study, ceramic foams were produced using starch consolidation casting method. This research focused on the preparation of alumina-based ceramic foam by using corn starch as a pore-forming agent. Preparation of alumina based ceramic foam is studied to observe the effect of the addition of corn starch on its physical, mechanical and morphological properties. The composition of the suspension used included 64–58 wt.% alumina, 55 wt.% deionised water and other materials, such as silica and polyethylene glycol (PEG), were used as additive and dispersing agent respectively. Corn starch was added at 4, 6, 8 and 10 wt.%. The samples were preheated for gelation and coagulation processes, then dried and sintered at 1250 °C for 2 h. The ceramic foam gave a linear shrinkage from 1.07% to 3.39%. The obtained flexural strength was between 0.594 and 1.996 MPa. The average total porosity ranged from 54.05% to 70.70%. This study found that the suitable amount of corn starch in alumina foam is 4 wt.% because the resulting porosity values and flexural strength are appropriate for ceramic foams.

Abstract: The spectroscopic performance of Er³⁺ doped glass at 0.55 mm emission contain different nanoparticles NPs have been comparatively evaluated. Glass containing 1.0 mol % of Er³⁺ doped with different NPs (Ag, Co and Fe ) have been prepared using melt quenching technique. X-ray diffraction analysis reveals the all the prepared samples are amorphous. The UV-Vis absorption spectra of all glasses show several prominent peaks at 525 nm, 660 nm, 801nm, 982 nm and 959 nm due to transition from ground state ⁴I_15/2 to different excited of ²H_11/2, ⁴F_9/2, ⁴I_9/2, ⁴I_11/2, and ⁴I1_3/2. The emission of Er³⁺ at 0.55 mm for glass contain Ag NP shows significant enhancement about 3 folds up to 0.6 mol%. On the other hand, the emission of Er³⁺ at 0.55 mm for glass containing Fe NPs and Co NPs intensely quench probably due to the energy-transfer from Er³⁺ ion to NPs and magnetic contributions.

Abstract: A laser cavity was constructed for excitation of erbium doped zinc tellurite glass rods embedded with various concentration of Ag nanoparticles. Central to the system is a Xenon flashlamp for optical pumping, and mirrors to amplify the light waves. The amorphousity of the glass rod was studied by X-ray diffraction and the existence of silver nanoparticles inside the glass was confirmed by high resolution transmission electron microscopy analysis. The photoluminescence properties and differential thermal analysis curve of the samples confirmed the compatibility of the rods as gain medium. The rods were successfully fabricated and incorporated inside the laser cavity. The output of the laser with erbium doped zinc tellurite glass rods embedded with Ag nanoparticles was characterized via spectrum analyser and was found that the spectrum dominated at line 473 nm and 506 nm. The beam profiler was utilized to detect and display the laser beam in 3D.

Abstract: Borotellurite glass had been widely applied in the field of optical communications and devices. In this work, holmium oxides doped borotellurite glass had been successfully fabricated via conventional melt-quenched technique. The structural properties of holmium doped tellurite glass were found using x-ray diffraction (XRD) method. The nonexistence of sharp peaks in XRD pattern shows that the inclusion of holmium tellurite glass leads to the formation long range of disorderness. The optical properties of the glass system such as refractive index and optical band gap energy are investigated using UV-Vis spectrophotometer. The value of refractive index is found in nonlinear trend along with holmium oxides concentration. It is found that the refractive index is more than 2 at 0.01, 0.03 and 0.04 of holmium concentrations. The optical band gap energy was found in similar trend with refractive index which is in nonlinear pattern.

Abstract: Modifying the physical and optical properties of zinc borotellurite glasses by controlling rare earth (RE) doping is important in order to obtain high quality glass. In this study, Samarium (Sm³⁺) doped zinc borotellurite glasses were successfully fabricated by using conventional melt-quenching technique with chemical composition (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%). The physical properties by mean of their density as well as molar volume were measured while the optical properties have been studied through UV-Vis spectroscopy in order to determine the optical band gap (E_opt) and Urbach energy (ΔΕ) of the glass system. Optical absorption spectra of the glass samples were recorded in the range 350 nm - 750 nm at room temperature. The amorphous nature of the glass was confirmed from X-ray diffraction techniques. The density and molar volume of the glass samples were found to vary with respect to Sm³⁺ ions content. The value of optical band gap, E_opt lies between 2.605 eV to 2.982 eV for the direct transition and 2.768 eV to 3.198 eV for the indirect transition respectively. Meanwhile, the Urbach energy, ΔE was observed in the range of 0.112 eV to 0.694 eV respectively. The physical and optical properties were found to be strongly affected by the varying concentration of Sm³⁺ ions. Some other results will be analysed and discussed in detail.

Abstract: Silica (SiO₂) foams have been widely applied in numerous fields, mainly filters and catalysts supports, due to their characteristics of high permeability, high porosity and specific surface area. In this study, foams of SiO₂ from rice husk ash (RHA) was fabricated via polymeric sponge replication method. Polymeric foam initially was used as template and dipped into SiO₂ slurry followed by drying and sintering to yield the replica of the original polymeric foam. Different solid loadings of SiO₂ as-derived from RHA (20 to 35 wt. %) slurry and sintering temperature of 1150 °C were applied. Phase identification and chemical composition of the green and sintered foams were conducted using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF). Morphological observations were performed using Scanning Electron Microscopy (SEM). Density and porosity of the SiO₂ foams were characterized using Archimedes method. Compressive strengths of the foams were determined as per ASTM C773-88 (1999). XRD analyses confirmed that the SiO₂ as derived from the RHA were of tridymite and cristobalite phases with as high as 93% purity, as confirmed by XRF analyses. The density of SiO₂ foams fabricated was in the range of 0.614 to 0.989 g/cm³, whereas the porosity values was in the range of 70% to 82%%. Compressive strengths were found to increase from 0.05 to 0.30 MPa respectively, proportionate with the increased SiO₂ solid loading. Excellent properties of the SiO₂ foams definitely signifies that the polymeric replication method is indeed a promising technique for SiO₂ as derived from RHA foam fabrication.

Abstract: The emergence of Dilute Magnetic Semiconductors (DMS) with a potentials for spintronic application have attracted much researches attention, special consideration has been given to ZnO semiconductor material due to its wide band gap of 3.37 eV, large exciting binding energy of 60 meV, moreover, its ferromagnetic behavior at room temperature when doped with transition metals. M_xZn_1-xO (M = Fe or Ni) nanoparticles were synthesized by microwave assisted synthesis method calcined at 600°C. The structural, morphological and magnetic properties of these nanoparticles were studied using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Vibrating Sample Magnetometer (VSM) respectively. Single phase Wurtzite hexagonal crystal structure was observed for the undoped and Fe doped ZnO nanoparticles with no any impurity, whereas Ni doped ZnO nanoparticles shows the formation of NiO impurities. The magnetic measurement reveals a diamagnetic behavior for the undoped ZnO meanwhile a clear room temperature ferromagnetism was observed for both Fe and Ni doped ZnO. Fe doped ZnO present a high saturation magnetization compared to Ni doped ZnO. However, Ni doped ZnO present high coercivity. The research was confirmed that Fe doped ZnO material will be good material combination for spintronic applications.

Abstract: High temperature superconductor Tl-1212 with nominal starting composition (Tl_0.85Cr_0.15)Sr₂CaCu₂O_7-δ was prepared with high purity oxide powders using a solid state reaction method. Small amounts of nickel-zinc ferrite nanoparticles (Ni_0.5Zn_0.5Fe₂O₄) at compositions 0.01, 0.02, 0.05 and 0.10 wt. % were added into Tl-1212 superconductors. The effect of Ni_0.5Zn_0.5Fe₂O₄ nanoparticles’ addition on the critical temperature (T_c), transport critical current density (J_c), phase formation, and morphology was studied. The samples were characterized using electrical resistance measurement, transport critical current density measurement, powder X-ray diffraction method (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Zero-resistance critical temperature (T_c-zero) was found to rise from 97 K to 99 K with increasing Ni_0.5Zn_0.5Fe₂O₄ nanoparticles concentration. The highest value recorded for transport critical current density (J_c) was 3,120 mA/cm² at 77 K, which exhibited by sample with 0.02 wt. % of Ni_0.5Zn_0.5Fe₂O₄ nanoparticles. All samples showed a dominant Tl-1212 phase and exhibited tetragonal lattice structure in the P4/mmm space group. SEM micrographs showed close-packed microstructure with low porosity. EDX mapping showed that Ni_0.5Zn_0.5Fe₂O₄ nanoparticles were well distributed in the Tl-1212 samples. This study demonstrated that Ni_0.5Zn_0.5Fe₂O₄ nanoparticles have functioned as effective flux pinning centers to Tl-1212 superconductors and thus significantly enhanced its J_c.

Abstract: Bi_1.6Pb_0.4Sr₂Ca_2-xEu_xCu₃O_δ cuprates superconductor doped with Eu nanoparticles (x = 0.0000, 0.0025, 0.0200 and 0.0500) were synthesized through conventional solid state reaction method. Crystalline sucrose was added during pelletization and burn at 400°C for two hours to create low density sample. The effect of doping Eu₂O₃ nanoparticles on the structural and superconducting properties by means of critical temperature (T_c), critical current density (J_c), X-ray diffraction (XRD) together with Field Emission Scanning Electron Microscopy (FESEM) and Alternating Current Susceptibility (ACS) were studied. Based on XRD analyses, the crystallographic structure has shown slightly changed from tetragonal to orthorhombic. The amount of 2223 phase gradually decreased with the increment of Eu concentration which indicates that Eu nanoparticles substitution favours the growth of 2212 phases. The resistivity measurements show that the highest T_c value for doped samples found at 90 K for x = 0.0025. The FESEM images showed that the plate-like grains become smaller and distributed randomly without specific alignment due to the increment of Eu concentration.