LiNbO 3 (LN) and LiTaO 3 (LT) materials of polar crystal structure exhibit a spontaneous polarization that can be changed by temperature. This phenomenon, commonly known as the pyroelectric effect, leads to the generation of surface charges that in turn are the source for a pyroelectrocatalytic or pyroelectrochemical activity of these materials described in this paper. It can also be regarded as a selective conversion of thermal via electrical to chemical energy based on the pyroelectric effect. In this context, we have investigated the impact of thermally excited pyroelectric LN and LT nano-and microcrystalline powder materials on the bacterium Escherichia coli in aqueous solutions. Powders have been prepared both by milling of commercially available single crystals and by precursorbased solution routes. Our results show that in dependence on the crystallite size and surface area of the pyroelectric particulate material in direct contact with the cells and/or their culture solution, a high antimicrobial activity can be achieved. On the basis of further experimental results of oxidative conversion of the fluorescent dye 2′,7′-dichlorofluorescin, a disinfection mechanism including the formation of reactive oxygen species at the pyroelectric particle surface is proposed. The phenomenon is discussed in analogy to the well-established photocatalytic disinfection mechanism.

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The precise quantification of the pyroelectric coefficient p is indispensable for the characterization of pyroelectric materials and the development of pyroelectric-based devices, such as radiation sensors or energy harvesters. A summary of the variety of techniques to measure p is given in the present review. It provides a classification after the thermal excitation and an outline of capabilities and drawbacks of the individual techniques. The main selection criteria are: the possibility to separate different contributions to the pyroelectric coefficient, to exclude thermally stimulated currents, the capability to measure p locally, and the requirement for metallic electrodes. This overview should enable the reader to choose the technique best suited for specific samples.

The disinfection of bacteria by thermally excited pyroelectric materials in aqueous environments provides opportunities for the development of new means of sanitization. However, little is known about the formation of reactive oxygen species (ROS) at the surface of the thermally excited pyroelectric materials. To investigate the pyroelectrically driven ROS generation we performed OH radical specific measurements of thermally stimulated barium titanate nanoparticles in contact with palladium nanoparticles. Through electron spin resonance measurements with the spin trap BMPO (5-tert-butoxycarbonyl 5-methyl-1-pyrroline n-oxide) and fluorescence spectroscopy of 7-hydroxycoumarin, OH radical generation was detected, which confirms the hypothesis of pyroelectric ROS production. Since pyroelectric potential changes are insufficient for direct electrochemical OH radical generation, we propose a two-step chargetransfer model facilitated by intermittent contact between the palladium and the pyroelectric nanoparticles and the pyroelectric effect as the driving force for charge transfer. ■ INTRODUCTIONCommercial water disinfection currently relies on chemical methods using chlorine-or ozone-based chemicals, whereas physical methods like thermal disinfection or ultraviolet radiation are less often employed. Due to their high oxidative potential, reactive oxygen species (ROS) are well suited as a physical means of disinfection. A completely new approach for creating ROS is the utilization of the pyroelectric effect, 1 which seems favorable when naturally occurring temperature changes can be employed for the excitation of the pyroelectric materials and, thus, offer an environmentally friendly method of water disinfection.In an aqueous solution the spontaneous polarization at the surface of a ferroelectric is screened, for example, by dissolved ions or dissociated water molecules. Changes in temperature trigger the pyroelectric effect. The imbalance of polarization and screening charges changes the effective surface potential. It was shown that these potential changes whether they stem from changes in temperature or strain can be used to drive electrochemistry between physisorbed molecular species. 1,2 For example Hong et al. demonstrated water splitting on mechanically excited surfaces of BaTiO 3 and ZnO. Gutmann et al. proposed that the observed water disinfection with thermally stimulated LiNbO 3 and LiTaO 3 is facilitated by production of ROS at the surface of the pyroelectric materials.Free radicals have high oxidation potentials, especially the OH radical whose oxidation potential is twice that of chlorine which is commonly used for disinfection. It is known that OH radicals can pull H atoms from C−H and S−H bonds and split aromatic rings. Living cells are damaged by radicals reacting with amino acids and DNA molecules. 3 Photocatalytic E. coli inactivation with TiO 2 showed cell damage caused by various ROS, such as OH radicals, hyperoxide radicals, and H 2 O 2 . 4 Basically ROS react immediately at the place of their ori...

We report on the diffusion behaviour of hydrogen through the 3D vacancy network of the LiMO3 structure.