Bismuth ferrite
Encyclopedia
Bismuth ferrite is an inorganic chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with a perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...

 structure. It is one of the most promising lead-free piezoelectric materials by exhibiting multiferroic properties at room temperature. Multiferroic materials exhibit ferroelectric or anti-ferroelectric properties in combination with ferromagnetic (or antiferromagnetic) properties in the same phase. As a result, an electric field can induce change in magnetization
Magnetization
In classical electromagnetism, magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material...

 and an external magnetic field can induce electric polarization. This phenomenon is known as the magnetoelectric effect (ME) effect and materials exhibiting this effect are called magnetoelectrics or seignetto magnets. Further proof of it being ferromagnetic is that it produces a hysteresis loop during ferroelectric characterization. The ability to couple to either the electric or the magnetic polarisation allows an additional degree of freedom in device designs.

However one of the major drawbacks of the material is its high current leakage. Therefore it allows current to pass through when a high voltage is applied. Attempts to improve the electrical properties have been made by doping it with rare earth elements such as lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...

 (La), samarium
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...

 (Sm), gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...

 (Gd), terbium
Terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...

 (Tb) and dysprosium
Dysprosium
Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...

 (Dy) etc. The dopant can be at the A site or the B site. A site being the edges of the perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...

 cell and the B site being the centre of the perovskite cell.

Solid-state reaction

The most common method is the solid state reaction method. Starting powders of Bi2O3 and Fe2O3 were weighed according to the formulae of BiFeO3.The powders were mixed using zirconia balls and ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 as the milling solvent. The mixture is then ball-milled for 24hrs. The mixture is then calcined in the range of 600 to 700 degree Celsius then sintered at around 800 to 900 degree Celsius. Other precursor materials can be acetates or hydroxides.[1-4]

Thin film deposition

Epitaxial BiFeO3 films grown on SrTiO3 with SrRuO3 as the epitaxial electrode using pulsed laser deposition
Pulsed laser deposition
Pulsed laser deposition is a thin film deposition technique where a high power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited...

 (PLD) revealed an enhancement of the ferroelectric polarization and related properties by more than an order of magnitude in comparison to bulk BiFeO3 http://www.sciencemag.org/cgi/content/abstract/299/5613/1719. The origin of the enhancement is the in-plane compressive stress imposed by the SrRuO3 electrode, which leads to a tetragonal distortion of the perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...

 lattice as opposed to the rhombohedral distortion of the bulk crystal.
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