Karl Wilhelm Sali Baedeker (3 February 1877 – 6 August 1914) was a German

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

, and a professor at the

University of Jena The University of Jena, officially the Friedrich Schiller University Jena (, abbreviated FSU, shortened form ''Uni Jena''), is a public research university located in Jena, Thuringia, Germany. The university was established in 1558 and is cou ...

. He was the grandson of Karl Baedeker, the founder of the

eponymous An eponym is a noun after which or for which someone or something is, or is believed to be, named. Adjectives derived from the word ''eponym'' include ''eponymous'' and ''eponymic''. Eponyms are commonly used for time periods, places, innovati ...

travel guide publishing house, and the son of Fritz Baedeker (1844 - 1925), who ran the same company from 1869 until his death in 1925. One of his scientific discoveries was that the

resistivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity i ...

of cuprous iodide (CuI) depended on its

stoichiometry Stoichiometry () is the relationships between the masses of reactants and Product (chemistry), products before, during, and following chemical reactions. Stoichiometry is based on the law of conservation of mass; the total mass of reactants must ...

. Thin films of the material became much more conductive when exposed to iodine vapor; the effect was reversible. This was the first example of doping a semiconductor to change its properties and also the discovery of transparent conductive materials. He also observed a

Hall effect The Hall effect is the production of a voltage, potential difference (the Hall voltage) across an electrical conductor that is wikt:transverse, transverse to an electric current in the conductor and to an applied magnetic field wikt:perpendicul ...

in transparent copper iodide thin films that had the reverse sign to that in copper, an observation of what was later to be known as conduction by

electron hole In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle denoting the lack of an electron at a position where one could exist in an atom or crystal structure, atomic lattice. Since in ...

s in

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

s. This observation was critical in developing the theory of electron conduction in solids. Along with his graduate student Karl Steinberg, Baedeker studied the effect of varying concentration of iodine on the electrical properties of copper iodide. He also is credited with making the first transparent conducting oxide (TCO) thin film,

cadmium oxide Cadmium oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with octahedral cation and anion centers. It occurs natur ...

(CdO), in 1907. TCOs are now ubiquitous in optoelectronics and a multibillion-dollar industry. Baedeker was

killed in action Killed in action (KIA) is a casualty classification generally used by militaries to describe the deaths of their personnel at the hands of enemy or hostile forces at the moment of action. The United States Department of Defense, for example, ...

in August 1914 during

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

at the Battle of Liège . His son, Karl Friedrich Baedeker revived the Baedeker publishing house after the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. In 2014, a conference on transparent conducting oxides was held in Leipzig to commemorate the centenary of Baedeker's death. A paper on the life and work of Baedeker was published in the proceedings of the meeting.Marius Grundman, "Karl Baedeker (1877-1914) and the discovery of transparent conductive materials", Physica Status Solidi A 212(7), 1409-1426 (2015), doi: 10.1002/pssa.201431921.

References

{{DEFAULTSORT:Baedeker, Karl 1877 births 1914 deaths 20th-century German physicists German military personnel killed in World War I People educated at the St. Thomas School, Leipzig