Ionic conductivity (denoted by λ) is the movement of ions through a solid material, a phenomenon central to solid-state ionics. It is denoted by λ and measured in siemens per meter (S/m). While perfect crystals of inorganic compounds are typically electrical insulators, ionic conduction arises when defects are introduced—either intrinsically through thermal activation or extrinsically via doping with aliovalent impurities. These defects enable ion migration by providing pathways through the crystal lattice. Solid ionic conductors, known as solid electrolytes, are critical components in technologies such as all-solid-state batteries, supercapacitors, fuel cells, and thin-film microelectronic devices. The ionic conductivity (σ) follows an Arrhenius-type relationship with temperature, governed by activation energy barriers influenced by crystal structure and defect chemistry. Ionic conduction is one mechanism of current.
Ion conductivity in the context of Cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a semipermeable biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space). The cell membrane is a lipid bilayer, usually consisting of phospholipids and glycolipids; eukaryotes and some archaea typically have sterols (such as cholesterol in animals) interspersed between them as well, maintaining appropriate membrane fluidity at various temperatures. The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as transporters, and peripheral proteins that attach to the surface of the cell membrane, acting as enzymes to facilitate interaction with the cell's environment. Glycolipids embedded in the outer lipid layer serve a similar purpose.
The cell membrane controls the movement of substances in and out of a cell, being selectively permeable to ions and organic molecules. In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity, and cell signaling and serve as the attachment surface for several extracellular structures, including the cell wall and the carbohydrate cell coat called the glycocalyx, as well as the intracellular network of protein fibers called the cytoskeleton. In the field of synthetic biology, cell membranes can be artificially reassembled.
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