Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fabrication, phase formation and microstructure of Ni4Nb2O9 ceramics by
  using two-stage sintering technique   The potential utilization of two-stage sintering for the production of highly
dense and pure nickel diniobate (Ni4Nb2O9) 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 NiNb2O6 tended to
form together with the desired Ni4Nb2O9 phase, depending on sintering
conditions. The optimization of sintering conditions could lead to a
single-phase Ni4Nb2O9 ceramics with orthorhombic structure. The ceramics doubly
sintered at 950/1250 {\deg}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 Ni4Nb2O9 ceramics. However, the grains were irregular in
shape when the samples are sintered at 1050/1250 {\deg}C. Two-stage sintering
was also found to enhance ferroelectric behavior of Ni4Nb2O9 ceramic.

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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: ao-sci