Fabrication, phase formation and microstructure of Ni4Nb2O9 ceramics fabricated by using the two-stage sintering technique

Abstract

The potential utilization of two-stage sintering for the production of highly dense and pure nickel diniobate (Ni 4 Nb 2 O 9 ) ceramics with low firing temperature was demonstrated. Effects of designed sintering conditions on phase formation, densification and microstructure of the ceramics were characterized by X-ray diffraction (XRD), Archimedes method and scanning electron microscopy (SEM), respectively. It has been found that minor phase of columbite NiNb 2 O 6 tended to form together with the desired Ni 4 Nb 2 O 9 phase, depending on sintering conditions. The optimization of sintering conditions could lead to a single-phase Ni 4 Nb 2 O 9 ceramics with orthorhombic structure. The ceramics doubly sintered at 950/1250 °C for 4 h exhibited maximum density value of  92%. Microstructures with denser angular grain-packing were generally found in both sets of the sintered Ni 4 Nb 2 O 9 ceramics. However, the grains were irregular in shape when the samples are sintered at 1050/1250 °C. Two-stage sintering was also found to enhance ferroelectric behavior of Ni 4 Nb 2 O 9 ceramic. PAC S no. 77-84 Bw

Compositional Complexity as a Design Principle for Stabilizing Magnetization Reversal in Corundum-Derived A4Nb2O9 Phases

“…After the identification of the phases, the lattice parameters were refined by means of the Fullprof software using the structures previously reported for Ni 4 Nb 2 O 9 and Co 4 Nb 2 O 9 as models. As usual in this system, 126-type oxides are often observed as impurities in very small quantities. Nevertheless, the reproducibility of the syntheses is very high, rather surprising, due to three elements distributed on two crystallographic sites and with different preferences for the two possible structures.…”