Recent advances in lithography technology and the spread of 3D printers allow us a facile fabrication of special materials with complicated microstructures. The materials are called “designed materials” or “architectured materials” and provide new opportunities for material development. These materials, which owing to their rationally designed architectures exhibit unusual properties at the micro- and nano-scales, are being widely exploited in the development of modern materials with customized and improved performance. Meta-materials are found to possess superior and unusual properties as regards static modulus (axial stress divided by axial strain), density, energy absorption, smart functionality, and negative Poisson’s ratio (NPR). However, in spite of recent developments, it has only been feasible to fabricate a few such meta-materials and to implement them in practical applications. Against such a backdrop, a broad review of the wide range of cellular auxetic structures for mechanical metamaterials available at our disposal and their potential application areas is important. Classified according to their geometrical configuration, this paper provides a review of cellular auxetic structures. The structures are presented with a view to tap into their potential abilities and leverage multidimensional fabrication advances to facilitate their application in industry. In this review, there is a special emphasis on state-of-the-art applications of these structures in important domains such as sensors and actuators, the medical industry, and defense while touching upon ways to accelerate the material development process.

The crystal structure of $\left(1-x\right)\left({\text{Na}}_{0.5}{\text{K}}_{0.5}\right){\text{NbO}}_3\text{-}x{\text{CaTiO}}_3$ ceramics began to change from orthorhombic to tetragonal at $x\ge 0.03$ , then became a morphotropic phase boundary in which both the orthogonal and tetragonal phases coexisted at $0.03<x<0.07$ , and was converted to tetragonal structure at $x\ge 0.07$ . The Curie temperature decreased with increasing $x$ and the specimen became a relaxor at $x\ge 0.03$ . A dense microstructure with large grains was developed at $0.04<x<0.07$ due to liquid phase sintering. The relative density, grain size, and liquid phase considerably influenced the piezoelectric properties of the specimens. High piezoelectric properties of $d_{33}=241$ , $k_p=0.41$ , and ${\epsilon }_3^T/{\epsilon }_o=1316$ were obtained from the 0.95NKN-0.05CT ceramics sintered at $1050°\text{C}$ for 2 h, indicating that the 0.95NKN-0.05 ceramic is a good candidate material for lead-free piezoelectric ceramics.

Pb(Zr,Ti)O₃ (PZT) based compositions have been challenging to texture or grow in a single crystal form due to the incongruent melting point of ZrO₂. Here we demonstrate the method for achieving 90% textured PZT-based ceramics and further show that it can provide highest known energy density in piezoelectric materials through enhancement of piezoelectric charge and voltage coefficients (d and g). Our method provides more than ∼5× increase in the ratio d(textured)/d(random). A giant magnitude of d·g coefficient with value of 59 000 × 10⁻¹⁵ m² N⁻¹ (comparable to that of the single crystal counterpart and 359% higher than that of the best commercial compositions) was obtained.

This study reports the experimental observation and analysis of self-biased magnetoelectric (ME) effect in three-phase laminates. The 2–2 L-T mode laminates were fabricated by attaching nickel (Ni) plates and ME particulate composite plates having 3–0 connectivity with $0.948{\text{Na}}_{0.5}{\text{K}}_{0.5}{\text{NbO}}_3–0.052{\text{LiSbO}}_3$ (NKNLS) matrix and ${\text{Ni}}_{0.8}{\text{Zn}}_{0.2}{\text{Fe}}_2{\text{O}}_4$ (NZF) dispersant. The presence of two types of ferromagnetic materials, Ni and NZF, results in built-in magnetic bias due to difference in their magnetic susceptibilities and coercivity. This built-in bias $\left({\text{H}}_{\text{bias}}\right)$ provides finite ME effect at zero applied magnetic dc field. The ME response of bending mode trilayer laminate NKNLS-NZF/Ni/NKNLS-NZF in off-resonance and on-resonance conditions was shown to be mathematical combination of the trilayers with configuration NKNLS-NZF/Ni/NKNLS-NZF and NKNLS/Ni/NKNLS representing contributions from magnetic interaction and bending strain.