A perovskite is any material with a crystal structure following the formula ABX3, which was first discovered as the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3). The mineral was first discovered in the Ural mountains of Russia by Gustav Rose in 1839 and named after Russian mineralogist L. A. Perovski (1792–1856). 'A' and 'B' are two positively charged ions (i.e. cations), often of very different sizes, and X is a negatively charged ion (an anion, frequently oxide) that bonds to both cations. The 'A' atoms are generally larger than the 'B' atoms. The ideal cubic structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold cuboctahedral coordination. Additional perovskite forms may exist where either/both the A and B sites have a configuration of A1x-1A2x and/or B1y-1B2y and the X may deviate from the ideal coordination configuration as ions within the A and B sites undergo changes in their oxidation states.
Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic in nanotechnology and materials science. When a quantum dot is illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy. In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conductance band. The excited electron can drop back into the valence band releasing its energy as light. This light emission (photoluminescence) is illustrated in the figure on the right. The color of that light depends on the energy difference between the conductance band and the valence band, or the transition between discrete energy states when the band structure is no longer well-defined in QDs.
Covellite is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.
Bismuth ferrite (BiFeO3, also commonly referred to as BFO in materials science) is an inorganic chemical compound with perovskite structure and one of the most promising multiferroic materials. The room-temperature phase of BiFeO3 is classed as rhombohedral belonging to the space group R3c. It is synthesized in bulk and thin film form and both its antiferromagnetic (G type ordering) Néel temperature (approximately 653 K) and ferroelectric Curie temperature are well above room temperature (approximately 1100K). Ferroelectric polarization occurs along the pseudocubic direction () with a magnitude of 90–95 μC/cm2.
Caesium cadmium bromide (Cs Cd Br3) is a synthetic crystalline material. It belongs to the AMX3 group (where A = alkali metal, M = bivalent metal, X = halogen ion). Unlike most other bromides, CsCdBr3 is non-hygroscopic, giving it applications as an efficient upconversion material in solar cells. As a single crystal structure doped with rare-earth ions, it can be also used as active laser medium. It is highly transparent in the visible and infrared regions and can be used as a nonlinear optical crystal.
The thallium halides include monohalides, where thallium has oxidation state +1, trihalides in which thallium generally has oxidation state +3, and some intermediate halides containing thallium with mixed +1 and +3 oxidation states. These salts find use in specialized optical settings, such as focusing elements in research spectrophotometers. Compared to the more common zinc selenide-based optics, materials such as thallium bromoiodide enable transmission at longer wavelengths. In the infrared, this allows for measurements as low as 350 cm−1 (28 μm), whereas zinc selenide is opaque by 21.5 μm, and ZnSe optics are generally only usable to 650 cm−1 (15 μm).
Bismuth selenide is a gray compound of bismuth and selenium also known as bismuth(III) selenide.
Ruddlesden-Popper (RP) phases are a type of perovskite structure that consists of two-dimensional perovskite-like slabs interleaved with cations. The general formula of an RP phase is An+1BnX3n+1, where A and B are cations, X is an anion, and n is the number of octahedral layers in the perovskite-like stack. Generally, it has a phase structure that results from the intergrowth of perovskite-type and NaCl-type structures.
Sodium bismuth titanate or bismuth sodium titanium oxide (NBT or BNT) is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na0.5Bi0.5TiO3 or Bi0.5Na0.5TiO3. This compound adopts the perovskite structure.
Bismuth polycations are polyatomic ions of the formula Bin+
x. They were originally observed in solutions of bismuth metal in molten bismuth chloride. It has since been found that these clusters are present in the solid state, particularly in salts where germanium tetrachloride or tetrachloroaluminate serve as the counteranions, but also in amorphous phases such as glasses and gels. Bismuth endows materials with a variety of interesting optical properties that can be tuned by changing the supporting material. Commonly-reported structures include the trigonal bipyramidal Bi3+
5 cluster, the octahedral Bi2+
6 cluster, the square antiprismatic Bi2+
8 cluster, and the tricapped trigonal prismatic Bi5+
9 cluster.
Maksym V. Kovalenko is a full professor of inorganic chemistry and the head of the Functional Inorganic Materials group at ETH Zurich. A part of the research activities of the group are conducted at Empa (Dübendorf). He is working in the fields of solid-state chemistry, quantum dots and other nanomaterials, surface chemistry, self-assembly, optical spectroscopy, optoelectronics and energy storage.
Perovskite nanocrystals are a class of semiconductor nanocrystals, which exhibit unique characteristics that separate them from traditional quantum dots. Perovskite nanocrystals have an ABX3 composition where A = cesium, methylammonium (MA), or formamidinium (FA); B = lead or tin; and X = chloride, bromide, or iodide.
Titanium(II) bromide is the inorganic compound with the formula TiBr2. It is a black micaceous solid. It adopts the cadmium iodide structure, featuring octahedral Ti(II) centers. It arises via the reaction of the elements:
A selenite fluoride is a chemical compound or salt that contains fluoride and selenite anions. These are mixed anion compounds. Some have third anions, including nitrate, molybdate, oxalate, selenate, silicate and tellurate.
High-entropy oxides (HEOs) are complex oxides that contain five or more principal metal cations and have a single-phase crystal structure. The first HEO, (MgNiCuCoZn)0.2O in a rock salt structure, was reported in 2015 by Rost et al. HEOs have been successfully synthesized in many structures, including fluorites, perovskites, and spinels. HEOs are currently being investigated for applications as functional materials.
The borate iodides are mixed anion compounds that contain both borate and iodide anions. They are in the borate halide family of compounds which also includes borate fluorides, borate chlorides, and borate bromides.
Silvia Vignolini is an Italian physicist who is Director of research at the Max Planck Institute of Colloids and Interfaces and Professor of Chemistry and Bio-materials in the Yusuf Hamied Department of Chemistry at the University of Cambridge. Her research investigates natural photonics structures, the self-assembly of cellulose and light propagation through complex structures. She was awarded the KINGFA young investigator award by the American Chemical Society and the Gibson-Fawcett Award in 2018.
Kyoung-Shin Choi (Korean: 최경신) is a professor of chemistry at the University of Wisconsin-Madison. Choi's research focuses on the electrochemical synthesis of electrode materials, for use in electrochemical and photoelectrochemical devices.
Dicaesium silver hexabromobismuthate is an inorganic compound with the formula Cs2AgBiBr6. Being a stable double perovskite material, it is applied to photocatalytic reduction of carbon dioxide.
Bromoantimonates are compounds containing anions composed of bromide (Br−) and antimony (Sb). They can be considered as double bromides, metallohalides or halometallates. They are in the category of halopnictates. Related compounds include the bromobismuthates, iodoantimonates, bromophosphates, and bromoarsenates.
