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Lanthanum Aluminate (LaAlO3)

General Introduction of LaAlO3:

Lanthanum aluminate crystals, with the chemical formula LaAlO3 (LAO), belong to the hexagonal system and have a distorted perovskite structure. Lanthanum aluminate crystals have excellent mechanical strength, thermal stability, and chemical stability, and exhibit good lattice compatibility with a variety of functional oxide materials, such as high-temperature superconducting and ferroelectric thin films.

The Czochralski (CZ) method is the primary method for producing high-quality lanthanum aluminate (LaAlO₃, LAO) single crystals. High-purity La₂O₃ and Al₂O₃ are mixed in a stoichiometric ratio and pre-sintered to achieve densification. The mixture is then melted in a crucible at approximately 2100°C in an inert atmosphere with a small amount of oxygen. A precisely oriented seed crystal is placed in contact with the melt surface and slowly pulled (approximately 0.5–2 mm/h) and rotated to achieve uniform composition and temperature distribution, yielding large, low-defect single crystals. After growth, the crystals are oxygen annealed to eliminate stress and oxygen defects, then directionally cut and precision polished to produce substrates suitable for epitaxial growth.

Physical and Chemical Properties of Lanthanum Aluminate Crystals:

Crystal name	Lithium niobate crystal	Crystal structure	Diamond
Lattice constant	At room temperature = 3.789 Å	Melting point	2080 ℃
Density	6.52 g/mL at 25°C (lit.)	Mohs hardness	6.5 Mohs
Molar mass	213.89 g/mol	Refractive index	2.0 @ 632.8nm
Dielectric constant	~25	Thermal expansion coefficient (/K)	10×10^-6/°C

Working Principle of LaAlO3

Lanthanum aluminate (LAO) has a perovskite structure with a lattice constant close to that of typical superconducting thin film materials (such as YBa₂Cu₃O₇₋δ, YBCO). Therefore, epitaxially growing high-temperature superconducting thin films on LAO substrates can significantly reduce the lattice strain and dislocation density of the epitaxial films, thereby ensuring high crystal quality and uniformity. Furthermore, LAO is a low-loss, high-dielectric-constant insulator, which results in virtually no energy absorption at microwave frequencies, helping to maintain the high quality factor (Q) in superconducting devices such as microwave resonators, filters, and quantum bits. Superconducting films grown epitaxially on LAO substrates form seamless, continuous current channels. Due to the zero-resistance nature of the superconducting material, microwave signals propagate through the thin films with virtually no energy loss, enabling highly efficient microwave device operation.

Production Process of LaAlO3

(1) Material preparation: Using high-purity lanthanum oxide and aluminum oxide as raw materials, the lanthanum aluminate crystal blank is grown in a high-temperature melt by the Czochralski method.

(2) Preliminary processing: The crystal blank is inspected for defects and quality, and cut according to the designed size after passing the inspection.

(3) Precision machining: Use processes such as grinding, fine grinding and chemical mechanical polishing to obtain substrates that meet dimensional tolerances and are smooth.

(4) Surface treatment: If necessary, surface cleaning or heating treatment can be performed in an ultra-high vacuum environment to optimize the epitaxial film growth conditions.

Application Areas

Lanthanum aluminate is an excellent substrate for growing high-temperature superconducting thin films. Superconducting films grown using lanthanum aluminate can be made into various superconducting microwave devices, such as microwave resonators, filters, power amplifiers, etc. The high-quality film interface provided by lanthanum aluminate ensures high Q value and low energy loss, and can be widely used in application fields such as scientific research and quantum information.

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