ORIGINAL PAPER Investigation of Annealing Temperature on Structural and Morphological Properties of Cr 2 O 3 Nanoparticles for Humidity Sensor Application P. Jayamurugan 1 • R. Mariappan 1 • K. Premnazeer 2 • S. Ashokan 3 • Y. V. Subba Rao 4 • N. V. S. S. Seshagiri Rao 4 • C. Shanmugapriya 5 Received: 25 December 2015 / Revised: 3 May 2017 / Published online: 20 June 2017 Ó Springer Science+Business Media New York 2017 Abstract Cr 2 O 3 nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temper- atures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr 2 O 3 varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr 2 O 3 nanoparticles at 400 nm. The humidity sensor of the Cr 2 O 3 nanoparticles was studied by two temperature method. 1000 °C annealed Cr 2 O 3 nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr 2 O 3 nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased. & P. Jayamurugan muruganjaya85@gmail.com 1 Department of Physics, Adhiyamaan College of Engineering, Hosur, Tamilnadu 635109, India 2 Department of Physics, Islamiah College (Autonomous), Newtown, Vaniyambadi, Tamil Nadu 635 752, India 3 Department of Physics, Bannari Amman Institute of Technology, Sathyamanglam, Erode, Tamilnadu 638 401, India 4 Department of Physics, Birla Institute of Technology and Science (BITS), Hyderabad Campus, Pilani, Hyderabad, Telangana State 500078, India 5 Department of Physics, Sona College of Technology, Salem, Tamilnadu, India 123 Sens Imaging (2017) 18:22 https://doi.org/10.1007/s11220-017-0170-y