Among the various transition-metal nitrides, TaN is a material that has potential for application in microelectronic components such as capacitors, thin-film resistors, and barrier materials that prevent the diffusion of copper into silicon [1
]. In addition, TaN has been used in high-temperature ceramic pressure sensors because of its good piezoresistive properties [3
]. Also, it is an attractive histocompatible material that can be used in artificial heart valves [4
]. Among the various tantalum nitride phases, cubic delta-tantalum nitride (δ
-TaN), with a NaCl-type structure (space group: Fm3m), exhibits excellent properties such as high hardness, stability at high temperature, and superconductivity [5
In general, it is difficult to produce δ
-TaN under ambient conditions since its formation requires high temperature and nitrogen pressure. According to the data reported in another study [6
-TaN is normally made at more than 1,600°C and 16 MPa of nitrogen pressure. Kieffer et al. synthesized cubic TaN by heating hexagonal TaN above 1,700°C at a N2
pressure of 6 atm [7
]. Matsumoto and Konuma were successful in producing cubic TaN by heating hexagonal TaN at a reduced pressure using a plasma jet [8
]. Mashimo et al. were able to transform hexagonal TaN into cubic TaN by both static compression and shock compression at high temperature [9
]. Cubic TaN in powder form was also synthesized by self-propagating high-temperature synthesis technique [10
]. In this process, the combustion of metallic tantalum from 350 to 400 MPa of nitrogen pressure resulted in micrometer size δ
-TaN at a temperature above 2,000°C.
More recently, two approaches, solid-state metathesis reaction and nitridation-thermal decomposition [12
], were adopted for the synthesis of nanosized particles of δ
-TaN. O’Loughlin et al. used the metathesis reaction of TaCl5
N and 12 mol of NaN3
to produce δ
]. The authors concluded that significant nitrogen pressure created by the addition of NaN3
enabled cubic-phase TaN to form, along with hexagonal Ta2
N. Solid-state metathesis reaction applied to the TaCl5
Cl mixture resulted in a bi-phase product at 650°C comprising both hexagonal and cubic phases of TaN [13
]. More recently, Liu et al. reported the synthesis of cubic δ
-TaN through homogenous reduction of TaCl5
with sodium in liquid ammonia, with a subsequent annealing process at 1,200°C to 1,400°C under high vacuum [14
]. Nitridation-thermal decomposition, a two-step process for the synthesis of cubic δ
-TaN, was also reported [15
]. In the first step, nanosized Ta2
was nitrided at 800°C for 8 h under an ammonia flow. The as-prepared product was then thermally decomposed at 1,000°C in nitrogen atmosphere, and cubic nanocrystalline δ
-TaN was obtained.
In most cases, the products prepared by the above-mentioned methods were often mixtures containing other compounds such as TaN0.5 or other nonstoichiometric phases. Therefore, synthesis inefficiency of cubic δ-TaN nanoparticles by known approaches coupled with the multiphase composition of products makes this topic challenging and scientifically attractive.
In this paper, an attractive and rapid approach for synthesizing cubic δ-TaN nanoparticles is developed. This approach includes the combustion of K2TaF7 + (5 + k)NaN3 + kNH4F exothermic mixture under nitrogen atmosphere and water purification of final products to produce cubic δ-TaN. The approach described in this study is simple and cost-effective for the large-scale production of δ-TaN.