LSAT is the most common name for the

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

lanthanum aluminate - strontium aluminium tantalate, which has the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

(LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 or its less common alternative: (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃. LSAT is a hard, optically transparent oxide of the elements

lanthanum Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

strontium Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...

and

tantalum Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...

. LSAT has the

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 , known as the perovskite (stru ...

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

, and its most common use is as a

single crystal In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no Grain boundary, grain bound ...

substrate for the growth of

epitaxial Epitaxy (prefix ''epi-'' means "on top of”) is 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 cry ...

thin films A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...

Background

LSAT was originally developed as a substrate for the growth of high T_c

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

s thin films, mostly of

yttrium barium copper oxide Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds that display high-temperature superconductivity; it includes the first material ever discovered to become superconducting above the boiling point of liquid nitrogen ...

(YBCO), for microwave device applications. The motivation for its development was to create a lattice-matched substrate with a similar

thermal expansion coefficient Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...

and no structural phase transition over a wide temperature range, spanning from the high temperatures used for the growth of cuprates, to the cryogenic temperatures where they are superconducting.

Properties

LSAT has a

Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

of 6.5, placing it between

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and the mineral

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

. Its relative dielectric constant is ~22 and it has a

of 8~10×10⁻⁶/K. The thermal conductivity of LSAT is 5.1 Wm⁻¹K⁻¹. LSAT's (cubic)

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 ...

of 3.868 Å makes it compatible for the growth of a wide range of

oxides with a relatively low strain. LSAT's melting temperature of 1,840C is lower compared to similar alternative substrates, such as LaAlO₃. This property enables the growth of LSAT single crystals using the

Czochralski process The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, plati ...

(CZ), which has commercial advantages.

Uses

LSAT is primarily used in its

form, typically as thin (≤1 mm) wafers. These wafers are used as a common substrate for

epitaxial growth Epitaxy (prefix ''epi-'' means "on top of”) is 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 cry ...

. LSAT substrates are popular for epitaxial oxides and their heterostructures, often in the study of

electron correlation Electronic correlation is the interaction between electrons in the electronic structure of a quantum system. The correlation energy is a measure of how much the movement of one electron is influenced by the presence of all other electrons. At ...

phenomena. Typical materials grown on LSAT substrates include

strontium titanate Strontium titanate is an oxide of strontium and titanium with the chemical formula strontium, Srtitanium, Tioxygen, O3. At room temperature, it is a centrosymmetric paraelectricity, paraelectric material with a Perovskite (structure), perovskite st ...

(SrTiO₃),

s (such as

YBCO Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds that display high-temperature superconductivity; it includes the first material ever discovered to become superconductivity, superconducting above the boiling point o ...

iron-based superconductor Iron-based superconductors (FeSC) are iron-containing chemical compounds whose superconducting properties were discovered in 2006. The first of such superconducting compounds belong to the group of oxypnictides, which was known since 1995. Until 2 ...

s (iron-pnictides), rare-earth manganites, rare-earth nickelates and others. Semiconductors such as

gallium nitride Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV af ...

can also be grown on LSAT. LSAT's usefulness as a substrate for the growth of such films stems from its high chemical and thermal stability, and very low electrical conductivity. The growth conditions for such epitaxial layers can cause some substrates to form high densities of defects that can alter their properties. One example is the tendency of

to form

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

vacancy defect In crystallography, a vacancy is a type of point defect in a crystal where an atom is missing from one of the lattice sites.Ehrhart, P. (1991) "Properties and interactions of atomic defects in metals and alloys", chapter 2, p. 88 in ''Landolt-B ...

s under high temperatures in high

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

. These defects result in considerable variations of its properties, including the increase of electrical conductivity and optical opacity. LSAT on the other hand, is stable in both oxidizing and fairly reducing environments in high temperatures, thus enabling a larger window for the processing and growth conditions.

References

{{aluminium compounds Lanthanum compounds Aluminium compounds Aluminates Inorganic compounds Perovskites

Background

Properties

Uses

See also

References