Diverse microstructures of monoclinic copper niobate (m-CuNbO3) were synthesized by solid-state reaction (900 degrees C, 3-12 h). FESEM data demonstrated that agglomerated clusters grew as an elongated grains which migrated to form web-shaped equiaxed structure and dissected to form individual equiaxed microstructure. With femtosecond laser excitation (800 nm, 150 fs), open aperture Z-scan data revealed the presence of two-photon absorption. The nonlinear refractive index (n(2)) toggled between positive and negative nonlinearity for different microstructures. Web-shaped equiaxed structure kindled both the nonlinear absorption (beta(eff) = 2.0 x10(-12) m/W), nonlinear refraction (n(2) = 3.16 x 10(-17) m(2)/W) and a strong optical limiting action (onset limiting threshold of 22.24 mu J/cm(2)). (C) 2017 Elsevier B.V. All rights reserved.