Strontium titanate

Crystal structure
__ Sr 2+      __ Ti 4+      __ O 2−
General
Surname	Strontium titanate
Ratio formula	SrTiO 3
Brief description	colorless crystalline powder
External identifiers / databases
CAS number 12060-59-2 EC number 235-044-1 ECHA InfoCard 100,031,846 PubChem 82899 Wikidata Q421340
properties
Molar mass	183.49 g mol −1
Physical state	firmly
density	5.12 g cm −3
Melting point	2060 ° C
solubility	almost insoluble in water
Refractive index	2.394 (620 nm)
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Strontium titanate is a chemical compound of strontium from the group of titanates .

Occurrence

Strontium titanate occurs naturally in the form of the very rare and only discovered in 1982 mineral tau sonite (after the Russian geologist Lev Vladimirovich Tauson ).

Extraction and presentation

Strontium titanate is obtained from strontium carbonate and titanium dioxide using a Verneuil process .

${\displaystyle {\ce {SrCO3 + TiO2 -> SrTiO3 + CO2 ^}}}$

properties

Strontium titanate has a cubic unit cell of the perovskite type with the space group Pm 3 m (space group no. 221) . The Ti ⁴⁺ cation is located in the center of the unit cell , the O ²⁻ anions are located on the surface centers and the Sr ²⁺ cations are located on the corners . Up to a temperature of 105 K it has a tetragonal crystal structure with the space group I 4 / mcm (No. 140) . An antiferrodistortive transition to the perovskite structure occurs above this. Strontium titanate has unusual physical properties. It is the only known compound that is ductile at low temperatures (minus 195 to 770 degrees Celsius) , brittle with increasing heat (770 to 1230 degrees Celsius) and ductile again at very high temperatures (1230 to 1530 degrees Celsius).

Strontium titanate is an indirect semiconductor with a band gap of 3.25 eV (and direct band gap of 3.75 eV) and is therefore transparent to visible light. At room temperature, strontium titanate has a high relative permittivity of approx. 300, which initially increases significantly on cooling, but then assumes a constant value of approx. 10 ⁴ at temperatures below 4 K (and does not diverge at the Curie temperature as with a ferroelectric ) . It is therefore a quantum paraelectric. Even with very low doping, strontium titanate becomes superconducting and, with increasing charge carrier density, shows a broad maximum of the superconducting transition temperature with a maximum value of approx. 0.3 K (in volume experiments) or approx. 0.5 K (in direct current resistance).

Strontium titanate single crystals show persistent photoconductivity at room temperature. After exposure, the free electron concentration increases by two orders of magnitude and remains elevated for days.

use

Due to its high refractive index, strontium titanate is used for optical components and as a window in the infrared range. Strontium titanate has the same perovskite crystal structure as many other oxides with properties of interest for applications (e.g. high-temperature superconductivity in cuprates) and is therefore a popular substrate for thin-film deposition of these materials.

In Soviet radionuclide batteries , strontium titanate with the strontium isotope ⁹⁰ Sr was used for terrestrial purposes.

At atomic lattice defects, strontium titanate has the properties of a semiconductor and is being tested in research as a memristor .

literature

• Michael Bäurer: Grain growth in strontium titanate . Univ.-Verlag Karlsruhe, Karlsruhe 2009, ISBN 978-3-86644-335-8 ( PDF ).
• Anissa Gunhold, Wolfgang Maus-Friedrichs, Karsten Gömann, Günter Borchardt: Strontium titanate: properties and possible uses as an oxygen sensor . In: TU Contact . No. May 12 , 2003, pp. 31-37 ( PDF ).

Individual evidence

1. ↑ ^{a b c} data sheet Strontium titanate, single crystal substrate, <100> from Sigma-Aldrich , accessed on December 1, 2019 ( PDF ).
2. ↑ Taşyürek, Lütfi & Sevim, Melike & Çaldıran, Zakir & Aydoğan, Şakir & Metin, Onder. (2018). The Synthesis of SrTiO ₃ Nanocubes and the Analysis of nearly ideal diode application of Ni / SrTiO ₃ nanocubes / n-Si heterojunctions. Materials Research Express. 5. doi: 10.1088 / 2053-1591 / aaa745 .
3. ↑ ^{a b} Entry on strontium titanate in the GESTIS substance database of the IFA , accessed on November 4, 2018 (JavaScript required)
4. ↑ Optical Properties of Zinc Oxide and Strontium Titanate Thin Films (PDF; 6.9 MB)
5. ↑ Webmineral: Tausonite
6. ↑ ^{a b c} Page no longer available , search in web archives: Investigation of imperfections in strontium titanate using the methods of optical absorption, luminescence and SHG  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 2.7 MB)  
7. ↑ World of Physics: No question of brittle - novel ceramics , article from March 12, 2003.
8. ↑ K. van Benthem, C. Elsässer, RH French: Bulk electronic structure of SrTiO ₃ : Experiment and theory . In: Journal of Applied Physics . tape 90 , no. 12 , December 15, 2001, ISSN  0021-8979 , p. 6156-6164 , doi : 10.1063 / 1.1415766 ( scitation.org [accessed May 25, 2020]).
9. ↑ KA Müller, H. Burkard: SrTiO ₃ : An intrinsic quantum para electric below 4 K . In: Physical Review B . tape 19 , no. 7 , April 1, 1979, ISSN  0163-1829 , pp. 3593-3602 , doi : 10.1103 / PhysRevB.19.3593 ( aps.org [accessed May 18, 2020]).
10. ↑ Clément Collignon, Xiao Lin, Carl Willem Rischau, Benoît Fauqué, Kamran Behnia: Metallicity and Superconductivity in Doped Strontium Titanate . In: Annu. Rev. Condens. Matter Phys. . 10, 2019, pp. 25-44. arxiv : 1804.07067 . doi : 10.1146 / annurev-conmatphys-031218-013144 .
11. ^ Marianne C. Tarun, Farida A. Selim, Matthew D. McCluskey: Persistent Photoconductivity in Strontium Titanate. In: Physical Review Letters . Volume 111, 2013, doi: 10.1103 / PhysRevLett.111.187403 .
12. ↑ Florencio Sanchez, Carmen Ocal, Josep Fontcuberta: Tailored surfaces of perovskite oxide substrates for conducted growth of thin films . In: Chemical Society Reviews . 43, 2014, p. 2272. doi : 10.1039 / c3cs60434a .
13. ↑ Rashid Alimov: radioisotopes Thermoelectric Generator. ( Memento of October 13, 2013 in the Internet Archive ) Belonia, April 2005, accessed on December 20, 2010.
14. ↑ techtransfer.ima.kit.edu: Movable spaces