Nanocrystalline spinel Ni x Cu 0.82x Zn 0.2 Fe 2 O 4 : a novel material for humidity sensing V. Jeseentharani • L. Reginamary • B. Jeyaraj • A. Dayalan • K. S. Nagaraja Received: 27 August 2011 / Accepted: 10 December 2011 / Published online: 29 December 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The humidity sensing property of the ferrite systems Ni x Cu 0.8-x Zn 0.2 Fe 2 O 4 with 0.0 B x B 0.8 (x = 0, 0.2, 0.4, 0.6, 0.8) was studied using the standard ceramic technique. The spinel structure of the compounds was confirmed by X-ray diffraction studies, BET study and surface morphology by scanning electron microscopy. The compounds were subjected to dc electrical conductivity studies at room temperature. The resistance measurements as a function of relative humidity (RH) in the range of 5–98% were done and the humidity sensing factors (S f = R 5% /R 95% ) were calculated. The composite NiCuZn- 3(x = 0.4) possessed the highest humidity sensing factor of 3051.9 ± 500, whilst CuZn–1 (x = 0) possessed the lowest humidity sensing factor of 45.3 ± 12. The other compounds possessed lower humidity sensing factors of 116.7 ± 35, 783.4 ± 160 and 416.2 ± 65 for x = 0.2, 0.6 and 0.8, respectively. Introduction Oxide ceramics are widely used for humidity sensing applications. Many chemical and physical phenomena that take place on the surface of metal oxide ceramics rely on the electronic surface conduction and its porous structure. For metal oxides this functionality is connected to the degree of non-stoichiometry and the presence of structural defects. The structure of spinel compounds contains a tet- rahedral framework with high density of defects and is semiconductive in nature [1, 2]. The measurement of humidity has received great attention due to the recognized importance of vapour concentration in many areas such as meteorology, medicine, industry and agriculture [3–5]. Its domestic applications include intelli- gent control of the living environment in buildings, cooking control for microwave ovens, intelligent control of laundry, etc. In the automobile industry, humidity sensors are used in rear window defoggers and motor assembly lines. In the medical field, humidity sensors are used in respiratory equipments, sterilizers, incubators, pharmaceutical pro- cessing and biological products. In agriculture, humidity sensors are used for greenhouse air-conditioning, plantation protection (dew prevention), soil moisture monitoring and cereal storage. In general, humidity sensors are used for humidity control in chemical gas purification, dryers, ovens, film desiccation, paper and textile production and food processing [6]. Thus, monitoring and controlling humidity becomes necessary for high product quality and human comfort [4]. The desirable characteristics of humidity sen- sors are high sensitivity, good chemical and thermal stability and short response time [7]. The relative humidity (RH), which is the ratio of actual vapour pressure to the saturated vapour pressure at a given temperature, is the most fre- quently used parameter to specify humidity. In general, a disc-type porous ceramic sensor would offer higher sensitivity towards humidity than a film-type one, probably due to larger capacity towards water adsorption [8, 9]. Bulk ceramic sensors based on porous materials show higher mechanical and chemical resistance [10, 11]. Ceramic sensors work based on the adsorption of water molecules in the pores. The response mechanism has been related to the adsorption of water molecules inside the pores and at the V. Jeseentharani  L. Reginamary  B. Jeyaraj  A. Dayalan  K. S. Nagaraja (&) Department of Chemistry, Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai 600 034, India e-mail: dr.ksnagaraja@gmail.com V. Jeseentharani e-mail: jeseentha@gmail.com 123 J Mater Sci (2012) 47:3529–3534 DOI 10.1007/s10853-011-6198-9