Lanthanum aluminate

Lanthanum aluminate
Properties
LaAlO3
Molar mass 213.89 g/mol
Appearance optically transparent, tan to brown
Density 6.52 g/cm^3
Melting point 2,080 °C (3,780 °F; 2,350 K)
Insoluble in mineral acids at 25 °C. Soluble in H3PO3 > 150 °C[1]
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Lanthanum aluminate is an inorganic compound with the formula LaAlO3, often abbreviated as LAO. It is an optically transparent ceramic oxide with a distorted perovskite structure.

Properties

Crystalline LaAlO3 has a relatively high relative dielectric constant of ~25. LAO's crystal structure is a rhombohedral distorted perovskite with a pseudocubic lattice parameter of 3.863 angstrom. Polished single crystal LAO surfaces show twin defects visible to the naked eye. LAO's (pseudocubic) lattice constant is virtually identical to that of the perovskite LSAT. However, LSAT offers several advantages over LAO, especially in terms of lower defect densities and a lower melting temperature, that allows LSAT to be grown by the Czochralski process (Cz).

Uses

Epitaxial thin films

Epitaxially grown thin films of LAO can serve various purposes for correlated electrons 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 (PLD) and molecular beam epitaxy (MBE).

A schematic cross-section of the 2DEG formed at LAO-STO interfaces

LAO-STO interfaces

The most important and common use for epitaxial LAO is at the lanthanum aluminate-strontium titanate interface. In 2004, it was discovered that when 4 or more unit cells of LAO are epitaxially grown on strontium titanate (SrTiO3, STO), a conductive 2-dimensional layer is formed at their interface.[2] Individually, LaAlO3 and SrTiO3 are non-magnetic insulators, yet LaAlO3/SrTiO3 interfaces exhibit electrical conductivity,[2] superconductivity,[3] ferromagnetism,[4] large negative in-plane magnetoresistance,[5] and giant persistent photoconductivity.[6] The study of how these properties emerge at the LaAlO3/SrTiO3 interface is a growing area of research in condensed matter physics.

Substrates

Single crystals of lanthanum aluminate are commercially available as a substrate for the epitaxial growth of perovskites,[1][7] and particularly for 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)[8]

See also

References

  1. ↑ 1.0 1.1 LaAlO3 specifications from the supplier MTI Corp.
  2. ↑ 2.0 2.1 Ohtomo; Hwang (29 Jan 2004). "A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface". Nature 427. Bibcode:2004Natur.427..423O. doi:10.1038/nature02308.
  3. ↑ Gariglio; Reyren, Caviglia, Triscone (31 March 2009). "Superconductivity at the LaAlO3/SrTiO3 interface". Journal of Physics: Condensed Matter 21. Bibcode:2009JPCM...21p4213G. doi:10.1088/0953-8984/21/16/164213.
  4. ↑ Bert; Kalisky, Bell, Kim, Hikita, Hwang, Moler (4 September 2011). "Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface". Nature Physics 7. arXiv:1108.3150. Bibcode:2011NatPh...7..767B. doi:10.1038/nphys2079.
  5. ↑ Ben Shalom; Sachs, Rakhmilevitch, Palevski, Dagan (26 March 2010). "Tuning Spin-Orbit Coupling and Superconductivity at the SrTiO3/LaAlO3 Interface: A Magnetotransport Study". Physical Review Letters 104 (12). arXiv:1001.0781. Bibcode:2010PhRvL.104l6802B. doi:10.1103/PhysRevLett.104.126802.
  6. ↑ Tebano, Antonello; E Fabbri; D Pergolesi; G Balestrino; E Traversa (19 January 2012). "Room-Temperature Giant Persistent Photoconductivity in SrTiO3/LaAlO3 Heterostructures". ACS Nano 6: 1278–1283. doi:10.1021/nn203991q.
  7. ↑ LaAlO3 specifications from the supplier SurfaceNet
  8. ↑ P. Sivasubramani et al. (2005). "Outdiffusion of La and Al from amorphous LaAlO3 in direct contact with Si (001)" (PDF). Applied Physics Letters 86: 201901. doi:10.1063/1.1928316.