Calcium copper titanate

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Calcium copper titanate
CCTO-square.tif
Identifiers
Properties
CaCu3Ti4O12
Molar mass 614.1789 g/mol
Appearancebrown solid
Density 4.7 g/cm3, solid
Melting point >1000 °C
Structure
Cubic
Im3, No. 204
a = 7.391 Å
Hazards
Safety data sheet External MSDS
NFPA 704 (fire diamond)
NFPA 704.svgFlammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
1
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Calcium copper titanate (also abbreviated CCTO, for calcium copper titanium oxide) is an inorganic compound with the formula CaCu3Ti4O12. It is noteworthy for its extremely large dielectric constant (effective relative permittivity) of in excess of 10,000 at room temperature. [1]

Contents

History

CCTO was first synthesized in 1967 by Alfred Deschanvres and his coworkers. While the structural features were known, no physical properties had been measured. In 2000, Mas Subramanian and his colleagues at DuPont Central R&D discovered that CCTO displayed a dielectric constant greater than 10,000, compared to the normal dielectric SrTiO3, which has a constant of 300 at room temperature. Since then, it has found widespread usage in capacitor applications.

Synthesis and structure

Most compounds which form this crystal structure are made under high-pressure conditions. Pure CCTO, however, can be easily synthesized by standard solid state methods via intimate mixtures of the metal carbonate and oxide precursors at temperatures between 1000 and 1200 °C.

4TiO2 + CaCO3 + 3CuO → CaCu3Ti4O12 + CO2

The CaCu3Ti4O12 structure type is derived from the cubic perovskite structure, by an octahedral tilting distortion as is GdFeO3. In both cases the distortion is driven by a mismatch between the size of the A-cations and the cubic ReO3 network. However, CaCu3Ti4O12 and GdFeO3 adopt different patterns of octahedral tilting (a−b+a− and a+a+a+ in Glazer notation). The octahedral tilting distortion associated with the GdFeO3 structure leads to a structure where all of the A-cation environments are identical. In contrast, the octahedral tilting distortion associated with the CaCu3Ti4O12 structure produces a structure where 75% of the A-cation sites (A" sites) have square planar coordination, while 25% of the A-cation sites remain 12 coordinate. The square planar sites are almost always filled by Jahn-Teller ion such as Cu2+ or Mn3+, while the A' site is always occupied by a larger ion. [2]

Dielectric properties

Using the Clausius-Mossotti relation, the calculated intrinsic dielectric constant should be 49. [3] However, CCTO exhibits a dielectric constant upwards of 10,200 at 1 MHz, with a low loss tangent until approximately 300 °C. [4] [5] In addition, the relative dielectric constant increases with decreasing frequency (in the range of 1 MHz to 1 kHz).

The colossal-dielectric phenomenon is attributed to a grain boundary (internal) barrier layer capacitance (IBLC) instead of an intrinsic property associated with the crystal structure. [1] [4] This barrier layer electrical microstructure with effective permittivity values in excess of 10, 000 can be fabricated by single-step processing in air at ∼1100 °C. CCTO is therefore an attractive option to the currently used BaTiO3-based materials which require complex, multistage processing routes to produce IBLCs of similar capacity. [6]

Because there is a large discrepancy between the observed dielectric constant and the calculated intrinsic constant, the true origin of this phenomenon is still under debate. [7]

Related Research Articles

Titanite Nesosilicate mineral

Titanite, or sphene (from the Greek sphenos (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium.

Dielectric Electrically poorly conducting or non-conducting, non-metallic substance of which charge carriers are generally not free to move

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.

High-temperature superconductivity Superconductive behavior at temperatures much higher than absolute zero

High-temperature superconductors are operatively defined as materials that behave as superconductors at temperatures above 77 K, the boiling point of liquid nitrogen, one of the simplest coolants in cryogenics. All superconducting materials known at ordinary pressures currently work far below ambient temperatures and therefore require cooling. The majority of high-temperature superconductors are ceramic materials. On the other hand, Metallic superconductors usually work below -200 °C: they are then called low-temperature superconductors. Metallic superconductors are also ordinary superconductors, since they were discovered and used before the high-temperature ones.

Perovskite (structure)

A perovskite is any material with a crystal structure similar to the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3). The mineral was first discovered in the Ural mountains of Russia by Gustav Rose in 1839 and named after Russian mineralogist L. A. Perovski (1792–1856). The general chemical formula for perovskite compounds is ABX3, where 'A' and 'B' are two cations, often of very different sizes, and X is an anion (frequently oxide) that bonds to both cations. The 'A' atoms are generally larger than the 'B' atoms. The ideal cubic structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold cuboctahedral coordination.

In chemistry, titanate usually refers to inorganic compounds composed of titanium oxides. Together with niobate, titanate salts form the Perovskite group.

Strontium titanate

Strontium titanate is an oxide of strontium and titanium with the chemical formula SrTiO3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase transition with a very large dielectric constant ~104 but remains paraelectric down to the lowest temperatures measured as a result of quantum fluctuations, making it a quantum paraelectric. It was long thought to be a wholly artificial material, until 1982 when its natural counterpart—discovered in Siberia and named tausonite—was recognised by the IMA. Tausonite remains an extremely rare mineral in nature, occurring as very tiny crystals. Its most important application has been in its synthesized form wherein it is occasionally encountered as a diamond simulant, in precision optics, in varistors, and in advanced ceramics.

Lead zirconate titanate

Lead zirconate titanate is an inorganic compound with the chemical formula Pb[ZrxTi1−x]O3 (0≤x≤1). Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the compound changes shape when an electric field is applied. It is used in a number of practical applications such as ultrasonic transducers and piezoelectric resonators. It is a white to off-white solid.

The Jahn–Teller effect is an important mechanism of spontaneous symmetry breaking in molecular and solid-state systems which has far-reaching consequences in different fields, and is responsible for a variety of phenomena in spectroscopy, stereochemistry, crystal chemistry, molecular and solid-state physics, and materials science. The effect is named for Hermann Arthur Jahn and Edward Teller, who first reported studies about it in 1937. The Jahn-Teller effect, and the related Renner-Teller effect, are discussed in Section 13.4 of the spectroscopy textbook by Bunker and Jensen.

Barium titanate

Barium titanate is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a ferroelectric ceramic material that exhibits the photorefractive effect and piezoelectric properties. It is used in capacitors, electromechanical transducers and nonlinear optics.

Perovskite Oxide mineral

Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (CaTiO3). Its name is also applied to the class of compounds which have the same type of crystal structure as CaTiO3 (XIIA2+VIB4+X2−3), known as the perovskite structure. Many different cations can be embedded in this structure, allowing the development of diverse engineered materials.

Calcium titanate

Calcium titanate is an inorganic compound with the chemical formula CaTiO3. As a mineral, it is called perovskite, named after Russian mineralogist, L. A. Perovski (1792-1856). It is a colourless, diamagnetic solid, although the mineral is often coloured owing to impurities.

Cuprospinel is a mineral that occurs naturally in Baie Verte, Newfoundland, Canada. The mineral was found in an exposed ore dump, on the property of Consolidated Rambler Mines Limited near Baie Verte, Newfoundland. The mineral was first characterized by Ernest Henry Nickel, a mineralogist with the Department of Energy, Mines and Resources in Australia, in 1973.

Quantum paraelectricity

Quantum paraelectricity is a type of incipient ferroelectricity where the onset of ferroelectric order is suppressed by quantum fluctuations. From the soft mode theory of ferroelectricity, this occurs when a ferroelectric instability is stabilized by quantum fluctuations. In this case the soft-mode frequency never becomes unstable as opposed to a regular ferroelectric.

Silicate perovskite is either (Mg,Fe)SiO3 (the magnesian end-member is called bridgmanite) or CaSiO3 (calcium silicate) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and mainly exist in the lower part of Earth's mantle, between about 670 and 2,700 km (420 and 1,680 mi) depth. They are thought to form the main mineral phases, together with ferropericlase.

Nickel(II) titanate is an inorganic compound with the chemical formula NiTiO3 nickel(II) titanate, also known as nickel titanium oxide, is a coordination compound between nickel(II), titanium(IV) and oxide ions. It has the appearance of a yellow powder. There are several methods of synthesis for nickel(II) titanate. The first method involves nickel(II) titanate's melting temperature of over 500 °C at which its precursor decomposes to give nickel(II) titanate as a residue. Nickel(II) titanate has been used as a catalyst for toluene oxidation. The second method involved using enthalpy and entropy on the reaction to synthesize nickel(II) titanate through its phase transition.

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.

Mas Subramanian

Munirpallam Appadorai "Mas" Subramanian, often known also as M. A. Subramanian or Munirpallam Subramanian, is a solid-state chemist at Oregon State University in Corvallis, Oregon, and currently holds both the titles of Distinguished Professor and Milton Harris Chair of Materials Science in the Department of Chemistry. His work in solid-state chemistry on structure-property relationships of inorganic compounds has led to the discovery of several novel functional materials, many of which have found usage in various applications. Subramanian has authored 360 research publications and holds 60 patents. His publications have received more than 28,000 citations.

Sodium bismuth titanate or bismuth sodium titanium oxide (NBT or BNT) is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na0.5Bi0.5TiO3 or Bi0.5Na0.5TiO3. This compound adopts the perovskite structure.

References

  1. 1 2 Subramanian, M. A.; Li, Dong; Duan, N.; Reisner, B. A.; Sleight, A. W. (2000-05-01). "High Dielectric Constant in ACu3Ti4O12 and ACu3Ti3FeO12 Phases". Journal of Solid State Chemistry. 151 (2): 323–325. Bibcode:2000JSSCh.151..323S. doi:10.1006/jssc.2000.8703.
  2. ↑ "CaCu3Ti4O12 (Perovskite)". chemistry.osu.edu. Archived from the original on 2016-09-19. Retrieved 2016-07-04.
  3. ↑ Shannon, R. D. (1993-01-01). "Dielectric polarizabilities of ions in oxides and fluorides". Journal of Applied Physics. 73 (1): 348–366. Bibcode:1993JAP....73..348S. doi:10.1063/1.353856. ISSN   0021-8979.
  4. 1 2 Subramanian, M. A.; Sleight, A. W. (2002-03-01). "ACu3Ti4O12 and ACu3Ru4O12 perovskites: high dielectric constants and valence degeneracy". Solid State Sciences. 4 (3): 347–351. Bibcode:2002SSSci...4..347S. doi:10.1016/S1293-2558(01)01262-6.
  5. ↑ Ramirez, A. P; Subramanian, M. A; Gardel, M; Blumberg, G; Li, D; Vogt, T; Shapiro, S. M (2000-06-19). "Giant dielectric constant response in a copper-titanate". Solid State Communications. 115 (5): 217–220. Bibcode:2000SSCom.115..217R. doi:10.1016/S0038-1098(00)00182-4.
  6. ↑ Sinclair, Derek C.; Adams, Timothy B.; Morrison, Finlay D.; West, Anthony R. (2002-03-25). "CaCu3Ti4O12: One-step internal barrier layer capacitor". Applied Physics Letters. 80 (12): 2153–2155. Bibcode:2002ApPhL..80.2153S. doi:10.1063/1.1463211. ISSN   0003-6951.
  7. ↑ Research in Progress 2010, the University of Sheffield.
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