Hydroxyapatite (HAp) biomaterial ceramic was synthesized by three different processing routes viz. wet chemical process, microwave irradiation process, and hydrothermal technique. The synthesized ceramic powders were characterized by SEM, XRD, FTIR and XPS techniques. The dielectric measurements were carried out as a function of frequency at room temperature and the preliminary study on CO gas sensing property of hydroxyapatite was investigated. The XRD pattern of the hydroxyapatite biomaterial revealed that hydroxyapatite ceramic has hexagonal structure. The average crystallite size was found to be in the range 31-54 nm. Absorption bands corresponding to phosphate and hydroxyl functional groups, which are characteristic of hydroxyapatite, were confirmed by FTIR. The dielectric constant was found to vary in the range 9-13 at room temperature. Hydroxyapatite can be used as CO gas sensor at an optimum temperature near 125°C. X-ray photoelectron spectroscopic studies showed the Ca/P ratio of 1⋅ ⋅63 for the HAp sample prepared by chemical process. The microwave irradiation technique yielded calcium rich HAp whereas calcium deficient HAp was obtained by hydrothermal method.

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Exploiting the photosensitive property of BiFeO 3 thin films, we demonstrated a resistive switching memory cell having low V set voltage (þ2.0 V), an ultrahigh ON/OFF ratio of $10 7 and a good retention time of more than 10 6 s. Synthesis conditions were optimized during a sol-gel-assisted spin-coating method to get phase-pure BiFeO 3 films on Al substrate, at room temperature. Current-voltage analysis revealed that during optical illumination, photon-induced charge carriers migrate towards their respective electrodes along grain boundaries under an externally applied field, which initiate a substantial shift in the normal V set of þ10.4 V to a lower voltage (þ2.0 V). The Poole-Frenkel emission at the metal/BiFeO 3 interface is proposed and the role of electronic reconstruction at the interface is further investigated. Thus the write process in BiFeO 3 -based resistive-switching devices can be modulated in a controlled manner, which has the potential for integrating current resistive switching (memristive) memory device technology towards exciting optomemristive device technology. 1 Introduction The concept of altering the resistance of metal oxide thin film under external electrical stress opened a new remarkable research area attractive for nextgeneration nonvolatile memories with scenarios including very high-density integration and multistate logic implementation [1][2][3][4]. Among the nonvolatile memories considered till now, the resistive random access memory (ReRAM), employ reversible resistive switching (RS) behavior, is increasingly important due to its simple structure, long retention time, small size, and fast switching speed [5,6]. The simplicity of the geometrical structures (metal/meal oxide/metal) makes the resistance switching extremely attractive and promising.Many transition-metal oxide (TMO) materials possess the RS behavior and among them perovskite materials also show excellent RS [5,7]. Recently, this phenomenon has also been found in BiFeO 3 (BFO) films [8][9][10]. Usually, BFO is an extensively studied multiferroic material, which exhibits ferroelectric and ferromagnetic behaviors simultaneously [11]. As to this, BFO has been widely studied since it exhibits a high Curie temperature (T c % 1100 K), a high N eel temperature (T N % 643 K) and a large remnant polarization over 90 mC cm

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