What Is Strontium Titanate?
Strontium titanate is a composite oxide of strontium and titanium.
It is also known as titanium trioxide (IV) strontium. Although strontium titanate is an artificial stone, it is similar to the natural mineral tauzonite in chemical composition. Strontium titanate was once considered a diamond substitute.
Despite its lower Mohs hardness of 6, compared to diamonds’ Mohs hardness of 10, it is prized for its brilliance, which is 4.3 times that of diamonds, and its fire (the dispersion of light into the spectrum of colors).
Applications of Strontium Titanate
1. Current Main Applications
Strontium titanate is widely used as a substrate for ferroelectric and superconducting thin films due to its typical perovskite structure. It plays a significant role in applied research as a substrate for Josephson devices and SQUIDs (superconducting quantum interference devices).
Additionally, it is utilized in ceramic capacitors, benefiting from its excellent dielectric and thermoelectric properties, and in varistors, sensors, and thermoelectric elements, as it can easily be converted into semiconductors with additives like niobium.
2. Future Applications
In recent years, strontium titanate has gained attention as a photocatalyst for hydrogen production. Its high stability under light irradiation and strong photoreduction power make it a promising candidate for photocatalysis using only sunlight.
Furthermore, strontium titanate is being developed as a novel substrate that combines metallic properties with high-grade perovskite-type oxide characteristics, opening up potential for unprecedented applications.
Properties of Strontium Titanate
1. Physical Properties
Strontium titanate is a white solid with the chemical formula SrTiO3. It has a molecular weight of 183.5 and a CAS number of 12060-59-2. Its melting point is approximately 1,900°C, with a density of 5.1 g/cm3. Data on flammability or oxidizability is not available.
The crystalline system is cubic, with a lattice constant of a=0.3905 nm, typically grown by the Bernoulli method. The dielectric constant is 310 (at 27°C, 1MHz), and the coefficient of thermal expansion is 11.1×10-6/℃ (from room temperature to 1,000°C). The phase transition temperature is 110 K, and the refractive index is 2.407 (at 589 nm).
2. Chemical Properties
It is insoluble in water and most solvents, and stable at room temperature when sealed. Strong oxidizing agents and strong acids should be avoided due to their hazardous interaction potential.
At room temperature, strontium titanate is a colorless cubic crystal with a perovskite-type structure. Below 110 K, it transforms into a tetragonal structure. When heated to high temperatures, it loses some oxygen, turns black, becomes electrically conductive, and exhibits piezoelectricity at low temperatures.
It is non-flammable and considered non-hazardous. In the event of a fire, there are no specific restrictions on fire extinguishing methods.
Other Information on Strontium Titanate
1. Safety
While considered non-hazardous and with no known effects on human health, appropriate personal protective equipment should be used to prevent exposure. In case of skin or eye contact, rinse immediately with running water and seek medical attention if discomfort persists.
Ensure work is conducted in areas with local exhaust ventilation or well-ventilated spaces, taking precautions against direct contact and inhalation of vapors and dust. Currently, no aqueous environmental toxicity, fish toxicity, bioaccumulation, or soil effects have been reported. Dispose of the product through a specialized contractor.
2. Band Gap
The band gap is a region in a crystal’s band structure where electrons cannot exist. Typical conductors, such as iron, copper, silver, gold, and aluminum, have no band gap.
Strontium titanate is an indirect transition insulator with a band gap of 3.2 eV. At room temperature, it does not show fluorescence when excited by ultraviolet light, but when excited at low temperatures, electrons, and holes form a self-bound state and emit light at 500 nm due to their coupling.