Growth and characterization of new semiorganic nonlinear optical and piezoelectric lithium sulfate monohydrate oxalate single crystals Harsh Yadav a , Nidhi Sinha b , Binay Kumar a, * a Crystal Lab, Department of Physics & Astrophysics, University of Delhi, Delhi 110007, India b Department of Physics & Electronics, SGTB Khalsa College, University of Delhi, Delhi 110007, India A R T I C L E I N F O Article history: Received 18 April 2014 Received in revised form 10 December 2014 Accepted 24 December 2014 Available online xxx Keywords: B. Crystal growth C. X-ray diffraction D. Dielectric properties D. Optical properties D. Piezoelectricity A B S T R A C T New semiorganic crystal of lithium sulfate monohydrate oxalate (LSO) for nonlinear application was synthesized by controlled slow evaporation method. The growth rate of various planes of the grown crystal was estimated by morphological study. Single crystal XRD analysis conﬁrmed that the crystal belongs to triclinic lattice with space group P1. High transparency (95%) with large band gap (4.57 eV) was analyzed by UV–vis studies. FTIR and Raman spectroscopy were used to identify various functional groups present in the LSO crystal. SHG efﬁciency was found to be equal to the KDP crystal. Thermal stability (up to 117.54  C) and melting point (242  C) of the crystal were studied by TG-DTA. In dielectric measurements, the value of dielectric constant decreases with increase in frequency. Hardness studies conﬁrmed soft nature of crystals. The piezoelectric coefﬁcient was found to be 6pC/N along [0 0 1]. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Non-linear optical (NLO) crystals have been found to have important applications in various optical devices. Frequency converter in the ﬁeld of non-linear optics demands a novel material for laser application with good optical response and wide transparency in UV region. The low contribution of lattice ions in second harmonic generation (SHG) efﬁciency is counted in inorganic crystal, whereas delocalized p electrons are responsible for higher SHG efﬁciency in organic crystal [1,2]. By considering the above intuition, a new class of NLO materials has emerged in the form of semi-organic crystal with the combined effect of both inorganic and organic class to achieve a higher SHG efﬁciency. Many times, a single organic materials do not show any optical properties due to the centro-symmetric nature but the scenario changes when it combines with asymmetric inorganic materials. By combining the inorganic material with organic material, the performance of the optical devices was improved for tuning the range of frequencies in NLO application. On the basis of molecular packing, oxalic acid is known to crystallize in two forms viz., a (orthorhombic) and b (monoclinic). Both forms are centro- symmetric in nature and therefore the possibility of NLO activity is ruled out [3]. LSO semiorganic crystals were grown by slow evaporation method and which crystallized in triclinic system with non-centrosymmetric space group P1. The promising NLO activity and piezoelectric properties of LSO crystal makes it a suitable candidate for image processing, ultrasonic transducers, impact detector and position sensors [4,5]. The morphological studies based on Bravais–Friedel–Donnay–Harker (BFDH) law computed for the LSO crystal and were found to be relevant with the experimentally observed growth rate of the various planes present in the crystal [6]. The Vickers microhardness investigation has been carried out on the grown crystal. We have calculated the hardness number (H v ) and Meyer index (n) to understand the hardness of the material [7]. Pure and doped lithium sulfate monohydrate (LSMH) crystals have been grown by different techniques with promising piezoelectric, pyroelectric and NLO properties [8,9]. The property of Lithium ion (also known as hard acid), showing a higher charge density in comparison to all alkali metal and its ability to combine easily with organic and inorganic complexes [10] is being used in various semiorganic crystals. Many lithium sulfate materials such as Glycine lithium sulfate, Lithium sulfate admixtured L-alanine (LSLA), Ethylene Diamine Tetra Acetate doped lithium sulfate monohydrate were reported in the literature showing improved SHG efﬁciency [11–13]. In this class of materials, lithium sulfate monohydrate oxalate is found to be a promising crystal for the optical and piezoelectric applications. In the present work, we * Corresponding author. Tel.: +91 9818168001. E-mail address: b3kumar69@yahoo.co.in (B. Kumar). http://dx.doi.org/10.1016/j.materresbull.2014.12.065 0025-5408/ ã 2014 Elsevier Ltd. All rights reserved. Materials Research Bulletin 64 (2015) 194–199 Contents lists available at ScienceDirect Materials Research Bulletin journa l homepage: www.elsevier.com/locate/matresbu