Increase Of Substitution Amount Research Articles

Y-Type Strontium Hexaferrite: the Role of Al Substitution, Structural, and Magnetic Consequence

In this study, Y-type Sr-hexaferrite nanoparticles with nominal chemical composition of Sr2Co2Fe12−y/2Al y/2O22 (y = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by a co-precipitation method. Crystal structure, morphology, and magnetic consequence of nanoparticles were characterized by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive analysis of X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM), respectively. XRD spectra revealed that the high-purity hexagonal Sr2Co2Fe12−y/2Al y/2O22 single phase was formed at synthesis temperature of 900 °C or 1 h. It was also found that the crystallite size of nanoparticles was increased from 32.8 to 37.6 nm by an increase in the substitution content. FE-SEM results showed that the particle size increased with an increase in aluminum ion substitution, and the morphology of particles was gradually turned from irregular platelet to pyramidal shapes. The FTIR analysis was employed to approve different bond modes which were structured. The VSM analysis showed that, with an increase in amount of substitution, the coercivity decreases from 456 to 98 Oe.

Electrochemical performance of AB2 metal hydride alloys measured at −40°C

The low-temperature (−40 °C) electrochemical performance of Y-, Si-, Fe-, Cu-, and Mo-partially substituted AB2 metal hydride alloys was studied. The surface area and catalytic ability of these alloys were obtained from the double-layer capacitance and the product of the double-layer capacitance and charge-transfer resistance from AC impedance measurement, respectively. With the increase in amount of substitution, the surface areas in these substituted alloys showed different degrees of increase: Y-addition exhibited the largest increase, followed by Si-addition, and then Cu-, Mo-, and Fe-additions. The surface catalytic abilities of Si-containing alloys were the highest and followed by those of Mo-containing alloys. Cu-, Y-, and Fe-additions reduced the surface catalytic ability. The resistance at −40 °C benefited from the incorporations of Si, Mo, and Y, and deteriorated with the incorporations of Cu and Fe. In the best scenario of a single element-substituted AB2 alloy, the resistance at −40 °C is still higher than that from a commercially available AB5 alloy. Since the contributions to the low temperature performance of AB2 alloys from various modifiers are not the same, the combination of several modifiers is possible for further optimization.

Study on magnetism of Pr0.45(Ca1−x Sr x )0.55MnO3 samples

The polycrystalline samples of Pr0.45(Ca1−x Sr x )0.55MnO3 (x = 0.0, 0.2, 0.4, 0.6) were prepared by solid-state reaction. Influence of Sr2+ substitution for Ca2+ at A site on magnetism was studied through the measurements of X-ray diffraction (XRD) spectrum, the magnetization-temperature (M-T) curves and electron spin resonance (ESR) curves. The results show that the magnetism strengthens and charge ordering weakens gradually with the increase of Sr2+ substitution amount, respectively. The transition of paramagnetism(PM)-antiferromagnetism(AFM) occurs below the transition temperature of charge ordering (T CO), and there is little ferromagnetic phase in the antiferromagnetic background at the lower temperature, which results in complex magnetic phases of the samples. Ferromagnetic clusters appear and grow larger with the increase of substitution amount. In addition, the reentrant spin-glass behavior appears at about 41 K. The magnetism phenomenon of the samples is mainly due to the competition between double exchange and Jahn-Teller coupling. The Jahn-Teller coupling becomes weak, and the double exchange wins the advantage in the competition with the increase of substitution amount, which leads to the magnetism variation of the system.