Niobates Nanowires: Synthesis, Characterization and Applications

Perovskite oxides such as alkaline niobates crystal possess many interesting properties including piezoelectricity, pyroelectricity, electro-optic and nonlinear optical response (Bhalla et al., 2000). The most common alkaline niobates material is lithium niobate (LiNbO3). Since the discovery of LiNbO3 ferroelectricity (Matthias & Remeika, 1949), its properties are widely exploited by electronic devices particularly in telecom applications (Wooten et al., 2000). Those devices are made from bulk or thin films material and serves as sensors, actuators, detectors or filters. Potassium niobate (KNbO3) is most known for its large nonlinear coefficients ideal for wavelength conversion like second-harmonic generation (SHG), sum frequency mixing, as material in optical parametric oscillator, or lead-free piezoceramics (Saito et al., 2004). Sodium niobate (NaNbO3), less studied than LiNbO3 and KNbO3, also belongs to the alkaline niobates. Generally associated with potassium, NaNbO3 is a very promising lead-free piezoelectric ceramics (Guo et al., 2004). Besides bulk and thin films structures, zero(0D) and one-dimensional (1D) alkaline niobates nanostructures were synthesized recently to combine the dimensional confinement with the other known properties of perovskite materials. Different synthesis routes have been explored to obtain 0D nanoparticles or nanoflakes from alkaline niobates such as mechano-chemical milling (Kong et al., 2008; Schwesyg et al., 2007), nonaqueous route (Niederberger et al., 2004), sol-gel method (L. H. Wang et al., 2007) or hydrothermal route (An et al., 2002). Almost simultaneously, anisotropic alkaline niobates 1D structure were synthesized with various methods such as template assisted pyrolysis resulting in regular arrays of tubes (Zhao et al., 2005), solution-phase synthesis resulting in rod-like structures (Wood et al., 2008), or hydrothermal route giving free-standing nanowires with high aspect ratio (Magrez et al., 2006). Up to now, the nanomaterials properties have been well characterized using standard materials sciences methods like X-ray diffraction (XRD), scanning electron (SEM) or transmission electron (TEM) microscopy. However, nonlinear optical or electro-optic properties have been rarely studied. Moreover, few applications have used these types of nanowires while combining the various physical properties of perovskite alkaline materials and the anisotropic shape at the nanoscale level. Nanometric SHG light probe manipulated by optical tweezers and capable of guiding light has been already demonstrated (Nakayama