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The coexistence of ferromagnetism and paramagnetism of T’-Pr2-xCexCuO4+α-δ (T’-PCCO) nanoparticles with x = 0, and 0.10 have been studied intensively in the normal state. All samples were synthesized by a chemically dissolved method using HNO3 as a dissolving agent. The calcination process was performed at 1000°C for 15 h in air and followed by reduction annealing at 700°C in argon atmosphere for 10 h. All samples were first characterized by an x-ray diffraction (XRD) measureemnts followed by Rietveld and Maximum Entropy Method (MEM) analyseis. The result confirms the Ce-dependence and reduction annealing effect on the electron density at around the Cu site. The magnetic characterization was performed by using vibration sample magnetometer (VSM) indicating weak ferromagnetic properties at x = 0 and dominant paramagnetic properties at x = 0.10 at room temperature. Moreover, the weak ferromagnetic feature seems to remain after the annealing process. This signifies the coexist of weak ferromagnetism and paramagnetism at the normal state due to a number of oxygen vacancies in the crystal structure.

This study aims at optimizing the utilization of fly ash (FA), rice husk ash (RHA), and fermipan for the production of lightweight environmentally friendly and fire-resistant geopolymer concrete. The geopolymer concretes were synthesized by alkaline activation method of FA added with RHA as light aggregate and fermipan as forming pores. The lowest density (1.55 g/cm3) of produced concrete was achieved with the addition of 26% of RHA and 6% of fermipan relative to the mass of FA. X-Ray Diffraction (XRD) indicates the formation of a new phase resulted from the reaction between fermipan and other oxides. The morphology of lightweight geopolymer was examined by Scanning Electron Microscopy (SEM). It was found that the matrix of the material consists of high volume of pores due to the inclusion of fermipan. The compressive strength of the lowest density sample was 16.56 MPa and fire resistance testing showed that this material was able to withstand temperature as a high as 1200°C.

Recently, the so-called room-temperature ferromagnetism in any nanoparticles has been studied intensively. It is well known that the properties of ferromagnetism and superconductivity are contradictory in a superconducting high-Tc cuprate. The existence of ferromagnetism in the nanoparticles has been suggested to occur on the surface. This magnetism has been expected to come from defects inducing magnetic moments on oxygen vacancies at the surface of the nanoparticles. This work is to observe magnetism in nanosized superconducting Pr2-xCexCuO4 (PCCO) with x = 0.15 by means of a superconducting quantum interference device (SQUID). The magnetization curves of the reduced PCCO nanoparticles with the superconducting transition temperature, Tc, of ~25 K have revealed that there is weak ferromagnetism observed at room temperature. The magnitude of magnetization could be enhanced by oxygen reduction annealing in vacuum with increasing annealing temperature. A non-linear magnetization occurring in the reduced PCCO nanoparticles through the vacuum annealing process is probably due to a strong oxygen reduction producing more oxygen vacancies in the T'-structure.