The characterization of the specific surface area is determined
by means of Brunauer–Emmet–Teller (BET) method.
Nitrogen physisorption measurements at 77K were performed
in a Micromeritics Tristar 3000 surface analyzer. The total volume
of pores was obtained from a single point adsorption
method at P/P0 = 0.999 and the pore size distribution from the
analysis of the desorption branch of the isotherms using the
Barrett–Joyner–Halenda (BJH) method.
Transmission electron microscopy (TEM) was used in order to
confirm the mesoporous structure ofthe sintered replicas by a JEOL
JEM 2010 (200 kV) electronic microscope.
The microstructure and thickness of the humidity sensors were
analyzed by scanning electron microscopy (SEM) using a ZEISS
AURIGA instrument.
X-ray diffraction (XRD) was performed in a Bruker D8 automated
diffractometer with Ni filter and Lynx Eye detector, to study
the crystallite and the periodic structure ofthe material.Wide angle
XRD spectra were recorded in the 2 range from 20◦ to 100◦ and
low angle XRD spectra from 0.5◦ to 3.5◦.
The sensors were electrically characterized by impedance
spectroscopy using a frequency response analyzer (Novocontrol
Alpha-A) in a range of frequencies from 1 MHz to 0.1 Hz and an AC
signal of 300 mV. Samples were placed in a Linkam chamber and
the humidity level was fixed with a commercial humidification system
(Bronkhorst) composed of a liquid flow controller (LFC) and a
controlled evaporator mixer (CEM) from 0 to 3 ml/min of H2O in a
temperature range from 30 to 90 ◦C.