Observation of Spin Reorientation Transitions in Lead and Titanium-Modified BiFeO3 Multiferroics

We report the synthesis and basic characterization details of bulk Bi1 − xPbxFe1 − xTixO3 (x = 0.05 and 0.1) polycrystalline samples, which have been synthesized using the conventional solid-state route. We studied the effects of partially doping of Pb and Ti ion on structural, vibrational, and magnetic properties of multiferroic BiFeO3. X-ray diffraction (XRD) was used for crystallographic studies, followed by Rietveld refinement, and phase formation of the compounds was confirmed, which indicates that the sample has rhombohedral (R3c, 100%) symmetry for x = 0.05 and R3c (98%) + P4mm (2%) symmetry for x = 0.1. X-ray absorption spectroscopy has been probed at Fe L2,3 and O K edges to determine the valence (charge) state of Fe in BiFeO3. Interestingly, the magnetic measurement results revealed the existence of spin reorientation transition in Pb and Ti-modified BiFeO3, which indicates that the BiFeO3 samples studied may find promising applications in memory and spintronic devices.

Design of Multifunctional Titania-Based Photocatalysts by Controlled Redox Reactions

This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduction of rutile by SiC in inert Ar atmosphere, followed by post-oxidation in air. The impacts of processing conditions on the phase composition and photocatalytic activity were evaluated using Taguchi planning. The XRD studies confirmed the presence of rutile/anatase mixtures in the post-oxidised samples. The results emphasise that pre-reduction and post-oxidation temperatures are critical in defining the phase composition, while post-oxidation time is relevant for the photocatalytic performance. Microstructural studies revealed the formation of core-shell particles, which can suppress the photocatalytic activity. The highest apparent reaction rate of the photodegradation of methylene blue was observed for the sample pre-reduced in Ar at 1300 °C for 5 h and then calcined in air at 400 °C for 25 h. Though its performance was ~1.6-times lower than that for the same amount of nanostructured industrial P25 photocatalyst, it was achieved in the material possessing 2–3 times lower surface area and containing ~50 mol% of SiO2 and SiC, thus demonstrating excellent prospects for further improvements.

Studies on multiferroic properties of single phasic Bi0.85Ho0.05Sm0.1FeO3 ceramics

Single-phase polycrystalline Bi[Formula: see text]Ho[Formula: see text]Sm[Formula: see text]FeO3 ceramic is prepared by conventional solid state route. The co-doping of Sm and Ho (via Bi site) in BiFeO3 controls the formation of secondary phases. The Rietveld refinement analysis shows an increasing trend in tilt angle due to the rotation of FeO6 octohedra with respect to host BiFeO3. The remanent polarization and the magnetization of Bi[Formula: see text]Ho[Formula: see text]Sm[Formula: see text]FeO3 ceramic are found to be significantly improved than BiFeO3 and Bi[Formula: see text]Sm[Formula: see text]FeO3 at room-temperature. Considerable variations in the remanent polarization (0.18 to 0.11 [Formula: see text]C/cm2) on magnetic poling and a dielectric anomaly in the vicinity of the antiferromagnetic transition temperature are due to the intrinsic magnetoelectric coupling effect in Bi[Formula: see text]Ho[Formula: see text]Sm[Formula: see text]FeO3 ceramic. The dielectric permittivity increases with increase in applied magnetic field and the coupling coefficient of Bi[Formula: see text]Ho[Formula: see text]Sm[Formula: see text]FeO3 ceramic is found to be 0.91% at 4 kOe.

Comparison of Structural and Electrical Behaviour of Phospho-Olivine LiNiPO4 and LiNi0.8Mn0.1Co0.1PO4 for High Voltage Rechargeable Li-Ion Batteries

Phase pure olivine LiNiPO4 and doped LiNi0.8Mn0.1Co0.1PO4 powders have been prepared by conventional solid state route. X-ray diffraction (XRD) combined with Rietveld refinements analysis reveals the formation of LiNiPO4 and doped LiNi0.8Mn0.1Co0.1PO4 with high crystalline nature at high temperature of 950 °C and 1000 °C. The lattice parameters of doped LiNi0.8Mn0.1Co0.1PO4 are significantly larger than LiNiPO4. It has been found out that the estimated crystallite size is in the order of nanometres for both samples. SEM analysis confirms that the particles have connected with each other in random shape and sub-microns size. The particle size has increased as small amount of Mn and Co are doped into LiNiPO4. The AC impedance spectroscopy measurements have revealed that the conductivity of LiNiPO4 is enhanced by around one order of magnitude by doping Mn and Co.

Effect of Ti-doping on the electrochemical performance of sodium vanadium(iii) phosphate

Na3V2−xTix(PO4)3 (x = 0.00, 0.05, 0.10, 0.15) was synthesized by a conventional solid-state route. Ti doping can effectively enhance the electrochemical performance of this tetragonal compound, especially under high charge–discharge rates.

Low-Fire Processing (1-x)Mg0.95Co0.05TiO3 - xCa0.6La0.8/3TiO3 Microwave Dielectric Ceramics

The effects of 3Z2B addition on the microwave dielectric properties and the microstructures of (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3ceramics prepared with conventional solid-state route have been investigated. Doping with 3Z2B can effectively promote the densification and the microwave dielectric properties of (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3ceramics. It was found that (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3ceramics can be sintered at 1150°C due to the liquid phase effect of 3Z2B additions observed by SEM. TheQ×fvalue of (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3ceramics decreased with increasing 3Z2B content. At 1150°C, 0.9(Mg0.95Co0.05)TiO3-0.1Ca0.6La0.8/3TiO3ceramics with 1.0wt% 3Z2B addition possesses a εrvalue of 22.6, a Qfvalue of 49,000 (GHz) and a τfvalue of-10.7 ppm/°C.

Effect of Sintering Behavior on Microwave Properties of (Ca0.8Sr0.2)ZrO3 Ceramics for Resonators

Microwave dielectric properties and microstructures of (Ca0.8Sr0.2)ZrO3 ceramics prepared by the conventional solid-state route have been studied. The values of the dielectric constant (εr) were 22-26. The Q×f values of 10400–11500 GHz were obtained when the sintering temperatures were in the range of 1400–1490°C. The temperature coefficient of the resonant frequency τf was not sensitive to the sintering temperature. The εr value of 26, the Q×f value of 11500 GHz, and the τf value of-9 ppm/°C were obtained for (Ca0.8Sr0.2)ZrO3 ceramics sintering at 1490°C. The ceramic, (Ca0.8Sr0.2)ZrO3 is proposed as a suitable candidate material for application in highly selective microwave ceramic passive components.

Effect of Sintering Behaviors on Microwave Dielectric Properties of (Ca0.3Sr0.1)Sm0.4TiO3 Ceramics

The microstructure and dielectric properties of the (Ca0.3Sr0.1)Sm0.4TiO3 ceramics with various sintering conditions have been investigated. The compounds were prepared by the conventional solid-state route with various sintering temperatures from 1340 to 1400°C and sintering duration from 3 h. The resultant microwave dielectric properties were analyzed based upon the densification, the X-ray diffraction patterns and the microstructures of the ceramics. The correlation between the microstructures, the microwave dielectric properties and sintering behaviors was also examined. The εr value of 96.7 and Q×f value of 11,600 GHz were obtained for (Ca0.3Sr0.1)Sm0.4TiO3 ceramics sintering at 1370°C for 3 h. The (Ca0.3Sr0.1)Sm0.4TiO3 ceramics had suitable dielectric properties can find applications in microwave devices such as resonator, filter and antenna.

Effect of Pressure Conditions on Characteristics of (Ca0.2Sr0.8)3Ti2O7 Dielectric Ceramics

The microwave dielectric properties of (Ca0.2Sr0.8)3Ti2O7 ceramic system have been investigated with various pressure conditions. The compounds were prepared by the conventional solid-state route with various pressure conditions from 60 to 80 Kg/cm2 and sintered at 1450oC for 4 h. The structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. The (Ca0.2Sr0.8)3Ti2O7 had excellent dielectric properties: Q×f ~ 50,000 (GHz) and εr ~ 63.2 for the sample at 70 Kg/cm2.