A. Chiorino et al., Preparation and characterization of SnO2 and MoOx-SnO2 nanosized powders for thick film gas sensors, SENS ACTU-B, 58(1-3), 1999, pp. 338-349
This work gives results about the characterization of SnO2 materials, prepa
red via the sol-gel route, pure and Mo6+-added. The materials were characte
rized as powders or thick films using a variety of techniques. The morpholo
gy of the powders was analyzed by XRD, SEM, TEM and HRTEM, their texture by
volumetric measurements. The morphology of the thick films was analyzed by
SEM. The goal of obtaining powders and films made by regularly shaped and
nanosized (30 divided by 50 nm) particles, even after thermal treatments at
850 degrees C is attained FT-IR spectroscopic and electrical measurements
were employed on powders and films, respectively, to obtain information on
the electronic effect due to the molybdenum addition. FT-IR results show th
at Mo lowers the intensity of the light scattered by free electrons and the
intensity of a broad absorption, previously assigned to the photoionizatio
n of V-o(+) [V-o(+) + h nu --> V-o(2) + e(-) (c.b.)]. Accordingly, electric
al data show that molybdenum markedly lowers (of about 2 orders of magnitud
e) the conductance of the films in air. Electrical measurements show that M
o lowers the response of tin oxide towards CO, but leaves almost unaltered
or enhances its ability to sense NO2, depending on the thermal pretreatment
s. Both pure and Mo-added materials treated at 650 degrees C show the same
response to NO2. However, fur the pure material treated at 850 degrees C th
e response to NO2 is halved, while it is almost unaffected by the thermal t
reatment on the Mo-added materials. The sensing temperature of maximum resp
onse is in My case 150 degrees C. FT-IR spectroscopy was also employed to o
btain information on the Ma species present on the surface of the materials
after treatments in oxygen and on how they are affected in the presence of
the different testing gases. Furthermore surface species formed by NO2 int
eraction were carefully investigated. (C) 1999 Elsevier Science S.A. All ri
ghts reserved.