Cuo2Edit

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CuO2 (copper oxide-related compounds and planes in cuprates)

Copper oxide chemistry spans a family of compounds with copper in various oxidation states and a central role in modern materials science. The notation CuO2 is encountered in several contexts: as a shorthand for copper(II) peroxide species in some chemical discussions, as a unit within copper-oxide planes in cuprate superconductors, and as a component in discussions of related oxides. The most common oxide encountered in everyday chemistry is copper(II) oxide, CuO, while CuO2 as a discrete, stable oxide is not a standard stoichiometric compound under ordinary conditions. In the context of cuprate superconductors, CuO2 denotes the planar units built from copper and oxygen that are essential to the electronic structure of the material. See also CuO and cuprate superconductors for broader context.

Nomenclature and structure

  • Primary oxide: The classic copper oxide CuO, also known as cupric oxide, is a monoclinic solid that forms as a stable oxide of copper on exposure to oxygen at elevated temperature. Detailed crystallography of CuO is described in studies of the monoclinic lattice and the local coordination geometry around the Cu2+ centers; CuO is often discussed in the context of its nonstoichiometry and defect chemistry. See CuO and monoclinic crystal system for more information.
  • CuO2 in cuprates: In high-temperature superconducting cuprates, copper and oxygen form planes of composition CuO2 that are essential to the materials’ electronic structure. These planes are typically embedded in layered oxide architectures with various spacer blocks (e.g., condensation of rare-earth or alkaline-earth layers). See cuprate superconductors and La2CuO4 for representative parent compounds.
  • Peroxide context: In some chemical discussions, CuO2 can refer to copper(II) peroxide species, which are generally less stable as discrete solids under ambient conditions and can exist transiently in reactions or on surfaces. See peroxide for broader context.

Physical and chemical properties

  • Oxidation states: In CuO, copper is in the +2 oxidation state. In cuprate planes, copper is formally in a +2 state locally, though the electronic structure is strongly influenced by hybridization with oxygen p orbitals and by electron correlations.
  • Structure: CuO adopts a monoclinic crystal structure with chains of edge-sharing CuO4 units in a distorted lattice. The CuO2 planes in cuprates typically feature square-planar or square-pyramidal coordination of Cu by O, arranged in a two-dimensional lattice that is central to their electronic behavior.
  • Electronic properties: CuO is a p-type semiconductor with a narrow band gap that depends on characterization method and sample quality. The CuO2 planes in cuprates give rise to low-dimensional electronic behavior, including strong electron correlations and, under appropriate conditions, superconductivity.
  • Physical manifestations: CuO and related oxides are dark-colored solids and can participate in redox chemistry through copper cycling between Cu2+ and Cu+ under suitable conditions.

Synthesis, preparation, and handling

  • Direct oxidation: Copper metal can be oxidized in air or controlled oxygen atmospheres to form CuO, especially at elevated temperatures. This is a common route to prepare CuO powders for pigments and catalysts.
  • Precipitation routes: CuO can be prepared by precipitation from copper salts (e.g., copper nitrate or copper sulfate) using basic media, followed by drying and calcination to obtain the oxide.
  • Precursors and hydroxyoxides: Copper hydroxide or basic copper carbonate precursors can decompose thermally to CuO. These routes are used in academic laboratories and industrial processes.
  • CuO2 contexts: In the study of cuprate superconductors, synthesis focuses on complex solid-state reactions that assemble the layered oxide structure with CuO2 planes, often involving high-temperature solid-state synthesis and oxygen annealing to achieve the desired doping and crystalline order. Representative examples of parent cuprates include La2CuO4 and YBa2Cu3O7.

Occurrence, applications, and impact

  • Pigments and catalysts: CuO is widely used as a pigment in ceramics and as a catalyst in oxidation reactions, including in environmental and chemical processing contexts. See copper oxide pigment and catalysis for related topics.
  • Energy storage: Copper oxides, including CuO, are explored as electrode materials in lithium-ion and sodium-ion batteries, where conversion and alloying reactions can yield high capacities. See lithium-ion battery and electrode materials for broader context.
  • Sensors and electronics: CuO-based materials are studied for gas sensing and optoelectronic applications, leveraging their semiconducting properties and surface reactivity.
  • CuO2 planes in superconductors: The CuO2 planes are central to the physics of cuprate superconductors. Doping of these planes (by chemical substitution or oxygen content adjustment) drives transitions from insulating to superconducting states in a family of materials known as cuprate superconductors; the mechanisms of pairing and superconductivity in these materials remain a topic of intense research and debate, discussed in sections on theory and experiment. See La2CuO4, YBa2Cu3O7, and Bi2Sr2CaCu2O8 for notable examples.

CuO2 planes and the superconductivity debate

  • Parent state and doping: The undoped cuprate parent compounds are typically Mott insulators with antiferromagnetic order. Introducing charge carriers via chemical substitution or oxygen content alters the electronic structure, and beyond a critical doping level, superconductivity emerges. This framework connects to broader concepts of Mott insulator physics and antiferromagnetism.
  • Pairing mechanisms: The dominant theoretical landscape for cuprates emphasizes electron-electron interactions and spin fluctuations as drivers of unconventional superconductivity, with d-wave pairing symmetry (often discussed under d-wave superconductivity). Competing theories consider the potential roles of phonons, charge order, and other many-body effects. See discussions under high-temperature superconductivity and d-wave.
  • Pseudogap and stripes: Experimental observations of a pseudogap and possible charge/spin stripe order in some cuprates have generated ongoing debates about the relationship between these phenomena and superconductivity. Reviews of these topics often present multiple viewpoints and interpretations, reflecting the complexity of correlated electron systems. See pseudogap and stripe order for more detail.
  • Representative materials: Notable cuprates that feature CuO2 planes include compounds such as La2CuO4 and YBa2Cu3O7 among others, each illustrating how the same structural motif can yield diverse electronic phases depending on composition and oxygen content. See cuprate superconductors for a broader overview.

Safety, environmental, and regulatory considerations

  • Toxicity: Copper oxides can be hazardous if ingested or inhaled as powders; proper handling and containment are important in laboratory and industrial settings. See hazardous materials and toxicology for general background on oxide particulates.
  • Environmental impact: As with many metal oxides, copper oxides can contribute to environmental contamination if released in large quantities. Appropriate waste management and recycling practices apply in industrial contexts.

See also