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As defined by the IUCr, a material is a crystal if it has essentially a sharp diffraction pattern. Crystalline materials are wide spread in our today's life. More than 98 % of the solid fraction of the earth comprises crystalline matter, most of which are oxides. Single-crystals in particular are the basis for many applications – lasers, LEDs, sensors, etc. – and play an important role in fundamental research – for instance in materials science. The discipline that elucidates the impact of the crystal structure on the physical properties of particularly crystalline materials – crystallography – is of specific importance for the design of new materials. Moreover, crystallography can be utilized to establish new concepts and thus may contribute solving today's challenges in science and technology. Several technologies exist for the conversion of electric energy into, e. g. heat, light and motion or vice versa. In this context, this work highlights an approach based on the crystal coupling phenomenon pyroelectricity that can be adopted for energy conversion concepts. By means of pyroelectric crystals, waste heat can be converted into surface charges, which provide a manifold of applications. First, a comprehensive overview of more than 3000 known pyroelectric materials is given, including a categorization in terms of properties and crystallographic characteristics. In order to provide a high pyroelectric coefficient at certain temperatures, taking economic, ecologic and further material properties into account, promising materials are suggested and verified by a computer controlled thermal/electrical stimulation set-up. Several possible applications as, for instance, disinfection [1], and anti-icing are presented. Finally, an approach to convert waste heat into chemical energy, i. e. the generation of hydrogen, is introduced.

In non-centrosymmetric crystalline matter, marked by the pyroelectric effect, a change in temperature alters the materials spontaneous polarization, which further changes the charge density on the material's surface. This results in a current flow trough an external circuit, which differs drastically at the boundary between two crystallographic phases. Therefore, pyroelectric materials offer a great potential of low-temperature waste heat recovery by utilizing e.g. the Olsen-Cylce to convert residual heat into electric energy. A previous characterization is necessary to determine the operating conditions of the active material. This work presents a method to evaluate temperature depended pyroelectric properties, especially the pyroelectric coefficient p and the phase transition temperture TC, with the help of a computer controlled thermal/electrical stimulation and a simultaneously recording of the electrical response of the material. Here, the analysis with the Sharp-Garn-method [1] separates the pyroelectric from eventually disturbing non-pyroelectric signal, enabling the characterization of p and TC over a broad spectrum of materials, ranging from inorganic single crystals and ceramics to organic polymers.

Energy conversion and storage has become the main challenge to satisfy the growing demand for renewable energy solutions as well as mobile applications. Nowadays, several technologies exist for the conversion of electric energy into e. g. heat, light and motion or vice versa. Among a large variety of storage concepts, the conversion of electrical in chemical energy is of great relevance in particular for location-independent use. Main factors that still limit the use of electrochemical cells are the volumetric and gravimetric energy density, cyclability as well as safety. The concept for a new thin-film rechargeable battery that possibly improves these properties is presented. In contrast to the widespread lithium-ion technology, the discussed battery is based on the redox reaction of multivalent Al-ions and their migration through solid electrolytes. The ion conduction and insertion processes in the crystalline materials of the suggested cell are discussed under a crystallographic point of view to identify suitable electrode and separator materials. A multilayer-stack of all-solid-state batteries is synthesized by pulsed laser deposition and investigated in situ, i. e. during charge and discharge, by X-ray reflection and diffraction methods. The correlation between crystal structure, morphology and electrical performance is investigated in order to characterize the ion diffusion and insertion process.

Because of their broad range of applications, electrochemical energy storage devices are the subject of a growing field of science and technology. Their unique features of high practical energy and power densities and low prices allow mobile and stationary applications. A large variety of electrochemical systems has been tailored for specific applications: Lithium-ion batteries for example have been optimized for mobile applications ranging from mobile phones to electric vehicles. On the other hand, sodium-sulphur accumulators – among others – have been developed for stationary applications to account for the capricious nature of renewable energies. Chemistry, physics and materials science have led to the optimization of existing cell-chemistries and the development of new concepts such as all-liquid or all-solid state batteries as well as high-energy density metal-air batteries. The aim of the BMBF (Federal Ministry of Education and Research, Germany)-financed project "CryPhysConcept" is to develop new concepts for electrochemical energy storage applying a crystallographic approach. First, a categorization of the main solid components of batteries based on their underlying working principles is suggested. Second, an algorithm for the identification of suitable new materials and material combinations, based on economical, ecological and material properties as well as crystallographic parameters, is presented. Based on these results, new concepts using multi-valent metal ions are proposed. Theoretical as well as experimental results including an iron-ion approach are presented.

Stoichiometric perovskite-type strontium titanate acts as an insulator because of its wide electronic band gap and has therefore great potential as high-k dielectric and storage material in memory applications. Degradation phenomena of insulating properties of transition metal oxides occur during long time voltage application. From the defect chemistry point of view the question arises how mobile species react on an external electric field and which impact the redistribution has on the stability of the crystal structure. Here, we discuss near-surface reversible structural changes in SrTiO3 single crystals caused by oxygen vacancy redistribution in an external electric field. We present in-situ X-ray diffraction during and after electroformation. Several reflections are monitored and show a tetragonal elongation of the cubic unit cell. Raman investigations were carried out to verify that the expansion involves a transition from the centrosymmetric to a less symmetric structure. Regarding a whole formation cycle, two different time scales occur: a slow one during the increase of the lattice constant and a fast one after switching off the electric field. Based on the experimental data we suggest a model containing the formation of a polar SrTiO3 unit cell stabilized by the electric field, which is referred to as migration-induced field-stabilized polar phase [1] at room temperature. As expected by a non-centrosymmetric crystal structure, pyroelectric properties will be presented in conjunction with temperature modulated electroformation cycles. Furthermore, we show that intrinsic defect separation establishes a non-equilibrium accompanied by an electromotive force. A comprehensive thermodynamic deduction in terms of theoretical energy and entropy calculations indicates an exergonic electrochemical reaction after the electric field is switched off. Based on that driving force the experimental and theoretical proof of concept of a solid-state SrTiO3 battery is reported.