Phase and morphology evolution of corundum-type Ni4Nb2O9 powders synthesized by solid-state reaction

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

“…1, it was obvious that the peaks of NiNb 2 O 6 phase were completely eliminated after using heating/cooling rates of 20 C/min. This finding was also consistent with our earlier work on Ni 4 Nb 2 O 9 powders system [7]. It was of interest to point out that for sintering temperature at 1350 C, a singlephase of Ni 4 Nb 2 O 9 (yield of 100% within the limitation of the XRD technique) already formed.…”

“…In this work, an evidence for the formation of Ni 4 Nb 2 O 9 phase, which coexisted with the NiNb 2 O 6 phase, is found after firing at temperature  1250-1300 C, similar to those reported earlier [7,8]. From Fig.…”

“…(1) has been applied to the XRD patterns, as given in Table 1. The results show that the desired Ni 4 Nb 2 O 9 phase has a corundum structure with an orthorhombic unit cell (a = 871.9 pm, b = 507.2 pm and c = 1428.9 pm, space group Pbcn (no.60)), which could be matched with JCPDS file number 46-0525 [11] and was similar to other works [7]. In addition, the unwanted phase of NiNb 2 O 6 , which is in agreement with literature [7,8] has a columbite structure with an orthorhombic unit cell (a = 1403 pm, b = 568.7 pm and c = 503.3 pm), consistent with JCPDS file number 76-2354 [12].…”

“…Recently, Liou et al prepared Ni 4 Nb 2 O 9 ceramics by the reaction-sintering process where a mixture of NiO and Nb 2 O 5 precursors were directly sintered into Ni 4 Nb 2 O 9 ceramics by bypassing calcination step. However, they found that minor NiO and NiNb 2 O 6 phases tended to form together with the Ni 4 Nb 2 O 9 phase, depending on sintering condition [7,8]. Thus, there has been a great deal of interest in the preparation of single-phase Ni 4 Nb 2 O 9 ceramic.…”

“…Thus, there has been a great deal of interest in the preparation of single-phase Ni 4 Nb 2 O 9 ceramic. In addition, the Ni 4 Nb 2 O 9 phase is very unstable, compared to the second phase that can easily be formed during preparation [7,8]. So far, these problems have been successfully resolved by applying a two-stage sintering technique in other similar systems where a potentially low-cost and simple ceramic fabrication to obtain highly dense and purely ceramics was demonstrated.…”