The ‘high entropy’ material was first introduced by Yeh et al for described high entropy alloys (HEA) which is composed of five or more metal elements in equimolar or near equimolar ratios[1]. An N-species material system with composition (xi) has ideal configurational entropy S[2]:
(1)
Maximum Smax is acquired at stoichiometric amounts, as xi =1/N for each i, hence:
In regard to a high entropy system, it is well known that configurational entropy is always not less than 1.61R[3].
Rost et al. extended the HEA concept to the field of ceramics and successfully synthesized a rock-salt structure (MgCoNiZnCu)O high entropy oxide (HEO) in 2015[2]. The HEO rock-salt phase has two different kinds of sublattices: the oxygen particles occupy the sites of face centered cubic lattice while the five kinds of cations locate at the octahedral gaps of the oxygen atoms randomly and uniformly[4,5]. Since then, HEO especially (MgCoNiZnCu)O has been thoroughly studied because of colossal dielectric constant[6], exceptional lithium-ion conductivity[7], excellent magnetic properties[8] and catalytic performance[9]. The incorporation of different metal cations in a single lattice structure, their possible synergistic effects, and the larger configurational entropy contribute to such multifunctional properties for this type of materials. Besides, much attention has been focused on synthesis of HEO and its derivatives[10], with methods including solid-state reaction[6], nebulized spray pyrolysis[4], flame spray pyrolysis[4], co-precipitation[11] and solution combustion method[12].
Among the large quantity of existing synthesis process for advanced ceramics, it is worth noting that ceramic injection molding (CIM) could overcomes limitations of conventional procedures due to a series of outstanding advantages. As a cost-effective near net shaping process, CIM attracts wide intention in recent years which could manufacture small, complex shaped, high dimensional precision ceramic compacts in enormous quantities[13–15]. This technology is usually comprised of four basic stages: compounding of feedstock, injection molding, debinding and sintering[16,17]. Feedstock of CIM usually consists of organic binders and ceramic powders. The binder system is a complex mixture composed of several components which is strictly selected to facilitated well injection properties and can be easily removed from green parts[18]. Binders used in CIM mainly consists of three functional components including: lubricants providing rheological properties for feedstock, macromolecular binders maintaining the shape integrity of green parts and debound compacts, as well as surfactants improving compatibility between ceramic powders and other organic binders[19]. CIM technology was used to fabricate a series of ceramic materials as follows: Al2O3[20,21], ZrO2[19,22], CaO[18], SiO2[23], MgAl2O4[24,25], SiC[26], B4C[27], AlN[13], Si3N4[28] and ZrB2[29] et al. Through this near net shaping CIM process, a large quantity of ceramic parts have been synthesized in recent years. Qin et al. [13] reported the CIM of complex shaped AlN ceramic with high thermal conductivity and successfully synthesized AlN heat sinks. Gromada et al. [30] have obtained materials allowed for the formation of ceramic cores with complicated shapes and high dimensional accuracy. While Hu et al. [20] fabricated a series of translucent alumina ceramics as prefabricated dental post, orthodontic dental ceramic bracket and relatively large size ceramic bowls using surface modificated alumina powders.
In accordance with the best of our authors’ knowledge, despite the previously described superiority of CIM technology, it has been never used to synthesize multi-components high entropy materials especially (MgCoNiZnCu)O HEO. In light of this aspect, a single rock-salt structure (MgCoNiZnCu)O was successfully synthesized for the first time using near net shaping CIM technology in present study. Besides, the Microstructure evolution of (MgCoNiZnCu)O was systematically discussed to provide process guidance for the future work about the synthesize of HEO through CIM.