Hybrid halide perovskites have become the “next big thing” in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH3NH3PbI3. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the “perovskite fever”, and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites f...

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises.

Synthesis, Structure, and Properties of Organic-Inorganic Perovskites and Related Materials

Organic–inorganic perovskites are a class of interesting compound in the perovskite family due to their unique structures of alternately stacking sheets of organic and inorganic components on the molecular scale. In this highlight, the basic knowledge and recent advances in organic–inorganic perovskites are reviewed with particular emphasis on the feature work including: the novel - and -oriented perovskite structures, synthesis, film preparation, patterning methods and optoelectronic properties of hybrid perovskites. Moreover, the small functional organic molecules can be templated into a regular arrangement by the inorganic perovskite framework. This unique material with nature-formed lamellar structure has the potential to be used as a template to create novel derivatives and bring about unique physical properties. Some interesting examples, such as intercalated polymer and silica network by topochemical polymerisation, fabrication of disk-like semiconductor nanocrystals and metal nanoparticles by hybrid perovskite templates are described.

Layered organic-inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering

Presently, a large variety of layered materials are synthesized that are able to intercalate neutral guest molecules or to exchange inorganic and organic ions for interlayer ions. Several of these materials are also found as minerals.

Intercalation and exchange reactions of clay minerals and non-clay layer compounds

Application of spin-spin relaxation to measurement of surface area and pore size distributions in a hydrating cement paste

Dynamics of the n-decylammonium chains in the perowskite-type Layer structure compound (C10H21NH3)2CdCl4

The deuteron and proton spin-lattice and spin-spin relaxation times T1 and T2 of adsorbed water in commercial portland cement and tricalcium silicate pastes were studied as functions of the hardening time at room temperature. The time dependence of the water self-diffusion coefficient of tricalcium silicate pastes was also followed. The proton and the deuteron T1 and T2 decrease markedly as hydration increases and the pastes harden due to the increase in the active surface and the number of adsorptive sites, thus providing convenient tools for studying the nature of the hydration process.

NMR Relaxation Study of Adsorbed Water in Cement and C3S Pastes

Pulsed proton NMR was used to determine the specific surface of hydrating cement pastes. The method is based on the fact that the measured proton spin-lattice relaxation rate (l/T1) of water in cement pastes is (in view of the fast exchange between water molecules in the adsorbed and bulk phase) proportional to the fraction of water molecules covering the solid surface and thus proportional to the NMR surface of the newly grown hydration products. In general, the method can be used for powders, fibrous and porous materials in contact with liquid water, or other fluids containing protons.

The Determination of Surface Development in Cement Pastes by Nuclear Magnetic Resonance

The temperature dependences of the second moments of the proton magnetic resonance absorption spectra and spin-lattice relaxation times are measured in (NH4)2HAsO4 and (NH4)2HPO4. Characteristic T1 minima and proton line width transitions are found demonstrating the existence of two chemically different NH4 groups in the unit cell. The anomalous increase in the As75 NQR frequency with increasing temperature in (NH4)2HAsO4 is explained as a result of thermally induced “acid” proton fluctuations in the HAsO4 groups.



In (NH4)2HAsO4 and (NH4)2HPO4 werden die Temperaturabhangigkeiten der zweiten Momente der magnetischen Protonenresonanzabsorptionsspektren und Spin—Gitter-Relaxationszeiten gemessen. Charakteristische T1-Minima und Ubergange der Protonenlinienbreiten werden gefunden und zeigen die Existenz von zwei chemisch verschiedenen NH4-Gruppen in der Einheitszelle an. Der anomale Anstieg in der As75-NQR-Frequenz mit steigender Temperatur in (NH4)2HAsO4 wird als Ergebnis thermisch induzierter „azider” Protonenfluktuationen in den HAsO4-Gruppen interpretiert.

G. Lahajnar

Papers

Dynamics of the n-decylammonium chains in the perowskite-type Layer structure compound (C10H21NH3)2CdCl4

NMR Relaxation Study of Adsorbed Water in Cement and C3S Pastes

The Determination of Surface Development in Cement Pastes by Nuclear Magnetic Resonance

Proton magnetic resonance study of molecular motion in (NH4)2HAsO4 and (NH4)2HPO4