Anomalous proton charge-transfer transport in nanostructured p-i-p+ multilayers

Functional electroceramics based on mixed oxyspinels are known to be
widely used for temperature-humidity measurements and control. The
main idea of this work is to develop high-reliable multilayers based
on such oxyspinel compounds for possible advanced industrial
application in environmental monitoring and energy saving using
nanostructured interlayer design of different conductive-isolating
ceramics. Temperature sensitive Cu0.1Ni0.1Co1.6Mn1.2O4- and
Cu0.1Ni0.8Co0.2Mn1.9O4-based pastes with p- and p+-type of electrical
conductivity were prepared by mixing powders of basic ceramics (the
sintered bulk ceramics were preliminary destroyed, wet-milled and
dried) with ecological glass powders (without PbO), inorganic binder
Bi2O3 and organic vehicle in one layer (p- and p+-type of electrical
conductivity) and p-р+ and p-р+-р-junction. The obtained p, p+
thick-films, double-layered p-р+ and triple-layered p-р+-р structures
possess promising electrical characteristics in the range of 298-368
К. The temperature constant were 3615 and 3830 K for p-р+ and
p-р+-р-junctions, respectively. Obviously, the increase of layer
numbers of these structures results in the improvement of their
temperature sensitivity. In addition, the p-р+-р-structure show
high-reliable temperature sensitive after additional ageing tests at
170 oC during 250 h without degradation, in contrast to single p- and
p+-type films. So thick-films in p-p+ and p-р+-р-junctions can be used
as high-reliable temperature sensitive structures for integrated
temperature/humidity sensors (especially, in p-i-p+ design, where i
denotes humidity-sensitive nanoporous magnesium aluminate MgAl2O4
compound). Anomalous proton charge-transfer processes caused by
simultameous influence of ambient temperature and humidity were first
discovered in the prepared nanostructured p-i-p+ multilayers. The
first of them, the effect unusual positive temperature coefficient of
resistance, was observed in p-i-p+ multilayers under temperature
increase beyond dew point. This effect is supposed to be caused by
water molecules transport between junction and environment
atmosphere. In this regime, the electrical characteristics of doublet
p-i and i-p+ multilayers are governed by hopping proton
charge-transfer within structurally intrinsic nanopores filled with
water. The second anomalous process, a so-called humidity-voltaic
effect, was observed as electric motion force generation caused by
orientation influence of separate electric fields of p-i and i-p+
multilayers. This effect was strongly dependent on technical
parameters of p-i-p+ nanostructure, reaching 0.1-0.2 V for typical
thick-film depths (near 20-25 m). The possibilities for practical
application of the above effects in energy storage-transfer devices
are discussed in details.