Solid State Phenomena Vol. 317

Abstract: La_0.7Ba_0.3Mn_1-xFe_xO₃ (x = 0 and 0.02) were prepared by using solid state synthesis method to investigate the effect of Fe³⁺ substitution at Mn-site on electrical behaviour and structural properties. An analysis of X-ray diffraction, XRD data using refinement method shown both x = 0 and x = 0.02 samples were in single phased and crystallized in rhombohedral structural with Pnma space group. From ρ vs T curves shown resistivity decreased under increased of applied current of 10 mA to 20 mA for both samples in the temperature range of 20 K-300 K. The larger electroresistance, ER effect observed for x = 0.02 in temperature range of 20 K – 180 K compared to x = 0 sample is suggested due to the development of filamentary conduction path under increased of applied current. It is suggested that Fe substitution enhanced magnetic inhomogeneity which contribute to the growth of formation of conductive path under increased of applied current, lead to increase of ER effect. In the temperature range of 180 K – 300 K, the observed decreased in ER for Fe substituted sample (x = 0.02) is suggested due to the increased of scattering effect and reduction of available hopping site in metallic region and insulating region, respectively. Restriction in the movement of charge carrier had weakened the ER effect for Fe substituted sample. The observed ER effect indicates the compound has a potential for application such as for non-volatile memory elements.

Abstract: The effect of Fe-substitution at the Mn-site in La_0.7Ca_0.3Mn_1-xFe_xO₃ (x = 0, 0.01, 0.03 and 0.05) on its structure, electrical and magnetic properties has been studied. These properties were investigated via X-ray diffraction (XRD) analysis, temperature-dependent resistance measurements and temperature-dependent AC magnetic susceptibility measurements. XRD analysis showed all samples are single phase materials. Temperature dependent resistance measurements between 30–300 K showed all samples to undergo insulator-metal transition as temperature decreases. Increase in Fe doping for x = 0, 0.01, 0.03 and 0.05 caused the transition temperature T_IM to decrease from 257 K, 244 K, 205 K and 162 K respectively. The magnetic susceptibility measurements showed the samples to exhibit paramagnetic to ferromagnetic transition as temperature decreased. Increase in Fe substitution x at the Mn-site progressively decreased the Curie temperature T_C from 250 K at x = 0 to 170 K at x = 0.05.

Abstract: The electroresistance, ER effect of La_0.85Ag_0.15Mn_1-xMo_xO₃ (x = 0.00 and 0.05) samples prepared using solid method are investigated. The increased of applied current from 5 mA to 10 mA does not change the metal-insulator transition temperature, T_MI for both samples however decreased the resistivity in the temperature region of 50 K – 300 K. Both samples exhibit large ER effect at low temperature region. At T_MI, the ER value is 75.5% (x =0) and decrease to 34.15% (x = 0.05). However, at 300 K, the value of ER increases to 57 % for Mo substituted sample, and the value decreases to 6.4% for the x =0 sample. The enhanced ER effect at 300 K may be due to the growth of conductive filaments under increased applied current. The increase of applied current may perturb the arrangement of magnetic inhomogeneity induced by Mo substitution, result in reduction of resistivity and lead to the observation of ER effect. These findings suggest potential application of La_0.85Ag_0.15Mn_1-xMo_xO₃ (x = 0.05) in spintronic devices.

Abstract: The microwave absorption properties of La_0.85Ag_0.15MnO₃ prepared by solid state method was investigated. Analysis of X-ray diffraction data using a refinement technique confirmed the rhombohedral structure of the samples. The microstructure of the sample characterised from field emission scanning electron microscope micrographs showed irregular grain shapes with grain sizes ranging from 800 to 1500 nm. M-H curves revealed the weak ferromagnetic properties of the sample at room temperature. The real and imaginary parts of permittivity and permeability as well as microwave reflection loss were measured by a vector network analyser in the 8–18 GHz frequency range. The La_0.85Ag_0.15MnO₃ sample showed a minimum reflection loss of –57.2 dB at 16.41 GHz, with a –10dB bandwidth (corresponding to reflection loss below –10 dB, or 90% absorption) of 2.67 GHz. The microwave absorption of La_­­­­_0.85Ag_0.15MnO₃ mainly arises from the conduction loss and domain wall motion which contributed to dielectric loss and magnetic loss, respectively.

Abstract: Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity. The band structure and thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ have been investigated. The bulk pellets were prepared from analytical grade ZnO, NiO and Fe₂O₃ powder using solid-state method. It was possible to obtain high thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ by controlling the ratios of dopants and the sintering temperature. XRD analysis showed that the fabricated samples have a single phase formation of cubic spinel structure. The thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ pellets improved with increasing Ni. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ (x = 0.0) is (0.515 x10^-3 Scm^-1). The band structure shows that Zn_xCu_1-xFe₂O₄ is an indirect band gap material with the valence band maximum (VBM) at M and conduction band minimum (CBM) at A. The band gap of Ni_(x)Zn_(1-x)Fe₂O₄ increased with increasing Ni content. The increasing band gap correlated with the lower electrical conductivity. The thermal conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The presence of Ni served to decrease thermal conductivity by 8 Wm^-1K^-1 over pure samples. The magnitude of the Seebeck coefficient for Ni_(x)Zn_(1-x)Fe₂O₄ pellets increased with increasing amounts of Ni. The figure of merit for Ni_(x)Zn_(1-x)Fe₂O₄ pellets and thin films was improved by increasing Ni due to its high Seebeck coefficient and low thermal conductivity.

Abstract: Composite La_0.88Bi_0.12Mn₀.₈₀Ni_0.20O₃ was synthesized using the conventional solid-state reaction method with sintering temperature of 1200 °C for 12 hours and the dielectric properties investigated. The X-ray diffraction result shows that the composite has a rhombohedral structure with lattice parameter of a = b = c = 5.5136 Ǻ. Scanning electron microscope shows grains with approximately from 0.8 to 5.4 μm in size with presence of voids. The dielectric permittivity, εʹ and dielectric loss, εʺ were measured in the range of 298 K to 473 K where both are temperature and frequency dependent. At 1 kHz to 100 kHz, the εʹ is around 10000 and the dielectric loss tangent, tan δ is below 1.5. The electric behavior of this composite is best represented by Quasi-dc model which consists of two universal capacitors in parallel. Parameters value from the fitting indicated that high correlations of electrons between inter and intra-clusters. The activation energy, E_a calculated from the conductivity of the sample gives a value of 0.116 eV. Vibrating sample magnetometer shows that the La_0.88Bi_0.12Mn₀.₈₀Ni_0.20O₃ has a magnetic coercivity, H_c of 36.109 G and retentivity, B_r, valued 2.7504 x 10^-3 emu/g.

Abstract: This study aims to synthesize microwave absorbent material from barium M-Hexaferrite doped Co-Mn-Ni ions (BaFe_12-2xCo_xMn_xNi_xO₁₉) using co-precipitation method with varying concentrations (x = 0.2, 0.4, 0.6, 0.8, and 1.0) and calcinations temperatures in the range of 200 to 800°C. The samples characterization was conducted to investigate the effect of doping concentration variations on the electrical, magnetic and microwave absorption properties using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM-EDX), Transmission Electron Microscope (TEM), Vibrating Sample Magnetometer (VSM), and Network Vector Analyzer (VNA). The results from XRD characterization showed that the sample formed the barium iron oxide (BaFe₁₂O₁₉) phase with a = b = 5.03Å and c = 13.43Å. The results of SEM-EDX and TEM samples of BaFe_9.6Co_0.8Mn_0.8Ni_0.8O₁₉ showed that the sample size ranged from 79-165 nm in the hexagonal crystal structure form. The magnetic properties with VSM indicate that the sample coercivity value decreases significantly from 0.41 T at x = 0.0 to 0.09 T at x = 0.8, indicating that the sample is soft magnetic. The value of electrical conductivity is in the range of 2.42 x 10^-4 to 9.30 x 10^-4 S/cm shows that the sample is a semiconductor. Analysis of the absorption properties of microwaves with VNA produced maximum permittivity and permeability values ​​of 28.40 and 54.40 at 10.30 GHz, and a maximum Reflection Loss (RL) value of -20.20 dB at a frequency of 15 GHz with an absorption coefficient of 99.05 % at concentration x = 0.6. The high permittivity, permeability, RL, and absorption coefficients indicate that the BaFe_12-2xCo_xMn_xNi_xO₁₉ sample has the potential to be a microwave absorbent material on X-band to Ku-band frequency.

Abstract: In this work, single phase Bismuth Ferrite, BiFeO₃ was successfully synthesized by using hydrothermal method assisted with different weight (0.24 g, 0.36 g and 0.48 g) of Chitosan. Potassium hydroxide (KOH) were used as a mineralizer during the synthesis process for the precipitation. The samples were characterized for different properties such as structural and optical properties, and were then compared with previous works. The X-ray diffraction data for all the samples showed that the samples had a single phase belonging to R3c space group with perovskite rhombohedral structure at diffraction angle 32.0° to 32.5° even though the slight presence of secondary phase at diffraction angle 28° was detected. Scanning electron microscope revealed a decrement in particle size as the weight of Chitosan increased indicating effective used of Chitosan in controlling the agglomeration of the particles. All samples BiFeO3 assisted with and without Chitosan showed significant enhancement in energy gap where the obtained results showed a small energy gap values ranging from ~1.22 eV to ~1.88 eV determined from UV-vis absorbance characterization. Therefore, by the addition of Chitosan, the properties of BiFeO₃ such as structural and optical have changed as well as preventing from the particle to agglomerate.

Abstract: In this work, (1-x) (Nd_0.67Sr_0.33MnO₃): x (TiO₂) composites with x = 0, 0.1, 0.2, 0.3 and 0.4 have been prepared to investigate the structural and electrical properties. Nd_0.67Sr_0.33MnO₃ (NSMO) was synthesised via the solid-state reaction method before incorporated with TiO₂. The addition of TiO₂ nanoparticle as the secondary phase in manganite composite would favour the spin-polarized tunnelling near to the grain boundary and thus enhance the extrinsic magnetoresistance. Nevertheless, nanoparticle addition might contribute to substitution and diffusion with manganite compound as reported in literature. The effect of the TiO₂ nanoparticle addition into NSMO composites has been examined by an X-ray diffractometer (XRD) and a four-point probe (4PP) system. From the thermogravimetric analysis (TGA), NSMO phase formation occurred in between 756.45 - 977.59 °C. XRD patterns showed that there is no peak shift when the TiO₂ concentration increases. It can be deduced that TiO₂ was segregated at the NSMO grain boundary region and its grain surface. However, a small amount of Ti atoms are expected to replace the Mn atoms in NSMO crystal system and has caused the increase in crystallite size. The electrical study showed that the presence of TiO₂ nanoparticle and substitution of Ti in Mn sites have weaken the double exchange (DE) mechanism and suppressed the metal-insulator transition temperature (T_MI). In addition, the insulating behaviour of TiO₂ has also caused the resistivity of composites to increase drastically.