Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Effect of laser irradiation on lithium niobate powders N.M. Ferreira a, ⁎ , M.C. Ferro b , M.P.F. Graça a , F.M. Costa a a i3N – Aveiro University, Physics Department, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal b CICECO – Aveiro University, Materials Engineering and Ceramic Department, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal ARTICLE INFO Keywords: LiNbO 3 Laser processing Structural characterization Radial thermal gradient Surfaces Powders ABSTRACT LiNbO 3 is a well-known material with high potential for many technological applications. However, conven- tional preparation techniques require high processing times at high temperatures. In this work, a new and fast approach is proposed, based on laser technology, envisaging obtaining bulk materials of LiNbO 3 . ´powders. The influence of the laser processing parameters, namely time and incident power beam, on the structure and morphology of the material was investigated and compared with the ones obtained from conventional heat treatment process. The results revealed a net dependence of LiNbO 3 crystals’ morphology with both laser power and irradiation time. Increasing the time of irradiation new crystalline phases are promoted (Li 3 NbO 4 , Li 0,585 NbO 3 and an “CaNb 2 O 6 ” isostructural type), which were also detected on samples prepared by the conventional heat treatment process in an air-atmosphere furnace. Moreover, similar morphologies can be also obtained using conventional heat treatment and laser processing. The expected characteristics of LiNbO 3 commercial powder (crystalline habit and size) were obtained for the based samples through laser irradiation under 6 W/1000 s and through heat-treatments under 1000 °C/24 h. The laser processing proved to be a suitable technique to form LiNbO 3 crystalline powders in a much more reduced time and also provides enough flexibility for tuning locally the grains size and morphology, allowing obtaining a morphological/structural radial gradient in a single step. 1. Introduction Nowadays, lasers are recognized as a versatile tool providing exceptional characteristic to process a wide range of materials. Among the many laser processing approaches, the most common are the laser cutting, laser welding, drilling, soldering, laser deposition, cleaning, structuring, polishing and crystals growth [1,2]. Despite laser materials processing had have a huge progress, being now at the forefront of some industrial applications, the use of laser treatment on oxides and glasses still is a subject not fully exploited and understood. Several studies have been done in order to realize the effect of such energy irradiation on the structure, morphology and consequently on the macroscopic properties of a wide variety of oxides, such as alumina, yttria, apatite–mullite glass-ceramics, calcium phosphate among others [1,3–12]. Notwithstanding, the laser processing on lithium niobate (LiNbO 3 ) still is an open topic since it has only been marginally exploited [13–15]. The interest on LiNbO 3 , which presents a rhombo- hedral crystalline structure, is due to its ferroelectric behavior , presenting a high Curie temperature (1210 °C) and being characterized by a large pyroelectric, piezoelectric, electro-optic and photo-elastic coefficients and it is naturally birefringent [13,14,16–22]. Due to this panoply of interesting properties it is already applied as waveguides, electro-optic devices as modulators and switches, frequency converter, acoustic-wave devices and holographic data storage, these are some examples [13,14,16–22]. Surface structuring of undoped lithium niobate by exposure to ultraviolet wavelengths, from a pulsed laser system, followed by etching was performed by Scott et al [13], showing that large-scale (mm sized) patterning can be achieved, using masks for wave guides applications [13]. Komatsu et al, present the pattern process of dots and lines of LiNbO 3 crystals on the surface of a 1CuO–40Li 2 O–32Nb 2 O 5 –28SiO 2 (% mol) glass using different laser irradiations. The feature of the laser- patterned LiNbO 3 crystal growth was examined using linearly polarized micro-Raman scattering measurements [14]. It was found that the c- axis orientation of LiNbO 3 crystals is placed in both dots and lines. The laser treatment, in a narrow width, induces a steep temperature gradient in the laser-irradiated region favoring a preferential growth orientation for the patterning of LiNbO 3 crystal lines with homoge- neous surface morphologies [14]. Another example of this preparation approach is on the LiNbO 3 crystallization through a CO 2 laser irradia- tion on a glass silicate [15]. However, increasing the power and exposure time of laser irradiation promotes the formation of SiO 2 http://dx.doi.org/10.1016/j.ceramint.2016.11.051 Received 5 October 2016; Received in revised form 7 November 2016; Accepted 7 November 2016 ⁎ Corresponding author. E-mail address: nmferreira@ua.pt (N.M. Ferreira). Ceramics International 43 (2017) 2504–2510 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Available online 14 November 2016 crossmark