Lanthanum aluminate is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...

with the formula LaAlO₃, often abbreviated as LAO. It is an optically transparent ceramic oxide with a distorted

perovskite structure 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 ...

Properties

Crystalline LaAlO₃ has a relatively high relative dielectric constant of ~25. LAO's crystal structure is a rhombohedral distorted

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as (XIIA2+VIB4+X2−3), known a ...

with a pseudocubic

lattice parameter A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has o ...

of 3.787

angstroms The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

at room temperature (although one source claims the lattice parameter is 3.82). Polished single crystal LAO surfaces show twin defects visible to the naked eye.

Uses

Epitaxial thin films

Epitaxially grown thin films of LAO can serve various purposes for

correlated electrons In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistic ...

heterostructures and devices. LAO is sometimes used as an epitaxial insulator between two conductive layers. Epitaxial LAO films can be grown by several methods, most commonly by

pulsed laser deposition Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique where a high-power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited. This material is vaporized from the t ...

(PLD) and

molecular beam epitaxy Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the dev ...

(MBE). LAO-STO interfaces The most important and common use for epitaxial LAO is at the

lanthanum aluminate-strontium titanate interface The interface between lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) is a notable materials interface because it exhibits properties not found in its constituent materials. Individually, LaAlO3 and SrTiO3 are non-magnetic insulators, ...

. In 2004, it was discovered that when 4 or more unit cells of LAO are epitaxially grown on

strontium titanate Strontium titanate is an oxide of strontium and titanium with the chemical formula Sr Ti O3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase ...

(SrTiO₃, STO), a conductive 2-dimensional layer is formed at their interface. Individually, LaAlO₃ and SrTiO₃ are non-magnetic

insulators Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work ...

, yet LaAlO₃/SrTiO₃ interfaces exhibit

electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

, superconductivity, ferromagnetism, large negative in-plane

magnetoresistance Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bu ...

, and giant persistent

photoconductivity Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation. Wh ...

. The study of how these properties emerge at the LaAlO₃/SrTiO₃ interface is a growing area of research in

condensed matter physics Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the ...

Substrates

Single crystals of lanthanum aluminate are commercially available as a substrate for the

epitaxial growth Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited crystalline film is called an epit ...

of perovskites,LaAlO₃ specifications from the supplier MTI Corp.
and particularly for

cuprate superconductor Cuprate superconductors are a family of high-temperature superconducting materials made of layers of copper oxides (CuO2) alternating with layers of other metal oxides, which act as charge reservoirs. At ambient pressure, cuprate superconductors ...

Non-epitaxial thin films

Thin films of lanthanum aluminate were considered as candidate materials for high-k dielectrics in the early-mid 2000s. Despite their attractive relative dielectric constant of ~25, they were not stable enough in contact with silicon at the relevant temperatures (~1000 °C).

References