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Perovskite

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Perovskite is a term used to describe both a specific mineral and a broad class of engineered materials. The namesake mineral is calcium titanium oxide, which has the chemical formula CaTiO3. It belongs to the orthorhombic crystal system, meaning its shape is slightly distorted from a perfect cube. This material is important because the perovskite structure can be adapted for many uses. Scientists use this structure to develop advanced technologies like solar panels and photodiodes. By changing the elements within the lattice, they can create materials with very specific properties.

Perovskite crystal structure (Yamanaka-Hirai-Komatsu 2002) crystallographic standard alignment
Perovskite crystal structure (Yamanaka-Hirai-Komatsu 2002) crystallographic standard alignment

The way these materials work depends on their unique crystal structure. A standard perovskite has a general formula of ABX3. In this arrangement, an A-site ion sits in the center of the lattice. This ion is usually an alkaline earth or a rare-earth element. B-site ions are located at the corners of the lattice. These are typically transition metal elements like titanium. The X-site ions, often oxygen or halogens, connect the B-site ions together. This creates a framework of octahedra, which are eight-sided shapes. The stability of this structure depends on the Goldschmidt tolerance factor, which must be between 0.75 and 1.0. If the ions do not fit perfectly, the structure may tilt or distort to stay stable.

There are several different types of perovskite structures. A major subclass is known as double perovskites, which have the formula A2B'B''O6. In these materials, two different types of cations occupy the B-sites. This creates a more complex and ordered pattern. These can form different arrangements like rock salt, columnar, or layered structures. Another way to categorize them is by their dimensions. 3D perovskites form corner-sharing octahedra networks. 2D perovskites form sheets of octahedra. 1D perovskites form chains, and 0D perovskites consist of isolated octahedra. As the dimensions decrease, the material's band gap increases.

YBa2Cu3O7-1994
YBa2Cu3O7-1994

The history of perovskite involves several important scientific discoveries. The natural mineral was first discovered in 1839 by Gustav Rose. He found it in the Ural Mountains of Russia. He named the mineral after the Russian mineralogist Lev Perovski. Later, in 1926, Victor Goldschmidt described the specific crystal structure. He did this through his work on tolerance factors. In 1945, Helen Dick Megaw published further details about the structure. She used X-ray diffraction data from barium titanate to provide more clarity. These steps allowed scientists to move from finding a rock to engineering a material.

Perovskites occur in many different environments across the universe. On Earth, the mineral is found in the mantle. It also appears in specific rocks at the Khibina Massif and in carbonate skarns at Magnet Cove, Arkansas. You can even find it in rocks ejected from Mount Vesuvius. In space, perovskite grains form in stars and brown dwarfs. These grains are responsible for the depletion of titanium oxide in the photosphere. This effect is very important for astronomers. In stars with low temperatures, the presence of titanium oxide helps define the transition between M-dwarf stars and L-dwarfs.

CsSnI3
CsSnI3

Modern research focuses on making these materials safer and more efficient. Many high-performing perovskites use lead, but lead can be toxic to the environment. To fix this, researchers are testing lead-free alternatives. They use elements like tin, germanium, bismuth, or antimony to replace the lead. Scientists are also studying chiral perovskites. These are materials that can interact with circularly polarized light. They are very useful for making light-emitting diodes (LEDs) and specialized photodetectors. The first 1D chiral perovskite crystal was found in 2003, and a 2D version followed in 2006.

Today, the study of perovskites connects mineralogy, chemistry, and physics. By understanding how ions fit into the A and B sites, engineers can tune the electronic behavior of the material. This includes managing how the material handles light and electricity. This process is called compositional tuning. It allows for the engineering of band gaps and carrier transport. This field of study is vital for the future of renewable energy and advanced electronics. The ability to control these tiny structures helps us turn sunlight into usable power more effectively.

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File:Perovskite crystal structure (Yamanaka-Hirai-Komatsu 2002) crystallographic standard alignment.png
Perovskite crystal structure...
File:YBa2Cu3O7-1994.png
YBa2Cu3O7-1994.png
File:CsSnI3.jpg
CsSnI3.jpg
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