Editing Cadmium arsenide (section)

== Properties ==

=== Thermal ===

Cd<sub>3</sub>As<sub>2</sub> dissociates between 220 and 280&nbsp;°C according to the reaction<ref>{{Cite journal | doi = 10.1021/j100785a028| title = Mass Spectrometric Study of the Nonstoichiometric Vaporization of Cadmium Arsenide<sup>1</sup>| journal = The Journal of Physical Chemistry| volume = 68| issue = 3| pages = 606–612| year = 1964| last1 = Westmore | first1 = J. B.| last2 = Mann | first2 = K. H.| last3 = Tickner | first3 = A. W.}}</ref>

:2 Cd<sub>3</sub>As<sub>2</sub>(s) → 6 Cd(g) + As<sub>4</sub>(g)

An [[activation energy|energy barrier]] was found for the nonstoichiometric vaporization of arsenic due to the irregularity of the partial pressures with temperature. The range of the energy gap is from 0.5 to 0.6 eV. Cd<sub>3</sub>As<sub>2</sub> melts at 716&nbsp;°C and changes phase at 615&nbsp;°C/<ref name=doi1073>{{Cite journal | doi = 10.1007/BF00551073| title = On the preparation, growth and properties of Cd<sub>3</sub>As<sub>2</sub>| journal = Journal of Materials Science| volume = 4| issue = 9| pages = 784–788| year = 1969| last1 = Hiscocks | first1 = S. E. R.| last2 = Elliott | first2 = C. T.| bibcode = 1969JMatS...4..784H| s2cid = 136483003}}</ref>

=== Phase transition ===

Pure cadmium arsenide undergoes several phase transitions at high temperatures, making phases labeled α (stable), α’, α”  (metastable),  and β.<ref>{{Cite journal | doi = 10.1107/S0567740869003323| title = A refinement of the crystal structure of α"-Cd<sub>3</sub>As<sub>2</sub>| journal = Acta Crystallographica Section B| volume = 25| issue = 5| pages = 988–990| year = 1969| last1 = Pietraszko | first1 = A.| last2 = Łukaszewicz | first2 = K.| doi-access = }}</ref> At 593° the polymorphic transition α → β occurs.

:α-Cd<sub>3</sub>As<sub>2</sub> ↔ α’-Cd<sub>3</sub>As<sub>2</sub> occurs at ~500 K.
:α’-Cd<sub>3</sub>As<sub>2</sub> ↔ α’’-Cd<sub>3</sub>As<sub>2</sub> occurs at ~742 K and is a regular first order phase transition with marked hysteresis loop.
:α”-Cd<sub>3</sub>As<sub>2</sub> ↔ β-Cd<sub>3</sub>As<sub>2</sub> occurs at 868 K.

Single crystal x-ray diffraction was used to determine the lattice parameters of Cd<sub>3</sub>As<sub>2</sub> between 23 and 700&nbsp;°C. Transition α → α′ occurs slowly and therefore is most likely an intermediate phase. Transition α′ → α″ occurs much faster than α → α′ and has very small thermal [[hysteresis]]. This transition results in a change in the fourfold axis of the tetragonal cell, causing [[crystal twinning]]. The width of the loop is independent of the rate of heating although it becomes narrower after several temperature cycles.<ref>{{Cite journal | doi = 10.1002/pssa.2210180234| title = Thermal expansion and phase transitions of Cd<sub>3</sub>As<sub>2</sub> and Zn<sub>3</sub>As<sub>2</sub>| journal = Physica Status Solidi A| volume = 18| issue = 2| pages = 723–730| year = 1973| last1 = Pietraszko | first1 = A.| last2 = Łukaszewicz | first2 = K.| bibcode = 1973PSSAR..18..723P}}</ref>

=== Electronic ===

The compound cadmium arsenide has a lower vapor pressure (0.8 atm) than both cadmium and arsenic separately. Cadmium arsenide does not decompose when it is vaporized and re-condensed. [[Semiconductor|Carrier Concentration]]  in Cd<sub>3</sub>As<sub>2</sub> are usually (1–4)×10<sup>18</sup> electrons/cm<sup>3</sup>. Despite having high carrier concentrations, the electron mobilities are also very high (up to 10,000&nbsp;cm<sup>2</sup>/(V·s) at room temperature).<ref>{{Cite journal | doi = 10.1002/pssb.2220940153| title = Inverted band structure of Cd<sub>3</sub>As<sub>2</sub>| journal = Physica Status Solidi B| volume = 94| pages = K57–K60| year = 1979| last1 = Dowgiałło-Plenkiewicz | first1 = B.| last2 = Plenkiewicz | first2 = P.| issue = 1| bibcode = 1979PSSBR..94...57D}}</ref>

In 2014 Cd<sub>3</sub>As<sub>2</sub> was shown to be a [[semimetal]] material analogous to [[graphene]] that exists in a 3D form that should be much easier to shape into electronic devices.<ref>{{Cite journal | doi = 10.1038/ncomms4786| pmid = 24807399| title = Observation of a three-dimensional topological Dirac semimetal phase in high-mobility Cd<sub>3</sub>As<sub>2</sub>| journal = Nature Communications| volume = 5| pages = 3786| year = 2014| last1 = Neupane | first1 = M. | last2 = Xu | first2 = S. Y. | last3 = Sankar | first3 = R. | last4 = Alidoust | first4 = N. | last5 = Bian | first5 = G. | last6 = Liu | first6 = C. | last7 = Belopolski | first7 = I. | last8 = Chang | first8 = T. R. | last9 = Jeng | first9 = H. T. | last10 = Lin | first10 = H. | last11 = Bansil | first11 = A. | last12 = Chou | first12 = F. | last13 = Hasan | first13 = M. Z. | bibcode = 2014NatCo...5.3786N| arxiv = 1309.7892 }}</ref><ref name=doi3990/> Three-dimensional (3D) topological Dirac semimetals (TDSs) are bulk analogues of [[graphene]] that also exhibit non-trivial topology in its electronic structure that shares similarities with topological insulators. Moreover, a TDS can potentially be driven into other exotic phases (such as Weyl semimetals, axion insulators and topological [[superconductor]]s), [[Angle-resolved photoemission spectroscopy]] revealed a pair of 3D [[Dirac fermion]]s in Cd<sub>3</sub>As<sub>2</sub>. Compared with other 3D TDSs, for example, β-cristobalite {{chem|Bi|O|2}} and {{chem|Na|3Bi}}, Cd<sub>3</sub>As<sub>2</sub> is stable and has much higher Fermi velocities. In situ doping was used to tune its Fermi energy.<ref name=doi3990>{{Cite journal | doi = 10.1038/nmat3990| pmid = 24859642| title = A stable three-dimensional topological Dirac semimetal Cd<sub>3</sub>As<sub>2</sub>| journal = Nature Materials| volume = 13| issue = 7| pages = 677–81| year = 2014| last1 = Liu | first1 = Z. K.| last2 = Jiang | first2 = J.| last3 = Zhou | first3 = B.| last4 = Wang | first4 = Z. J.| last5 = Zhang | first5 = Y.| last6 = Weng | first6 = H. M.| last7 = Prabhakaran | first7 = D.| last8 = Mo | first8 = S. K. | last9 = Peng | first9 = H.| last10 = Dudin | first10 = P.| last11 = Kim | first11 = T.| last12 = Hoesch | first12 = M.| last13 = Fang | first13 = Z.| last14 = Dai | first14 = X.| last15 = Shen | first15 = Z. X.| last16 = Feng | first16 = D. L.| last17 = Hussain | first17 = Z.| last18 = Chen | first18 = Y. L.| bibcode = 2014NatMa..13..677L}}</ref>

=== Conducting ===

Cadmium arsenide is a II-V [[semiconductor]] showing degenerate [[n-type semiconductor]] intrinsic conductivity with a large mobility, low effective mass and highly non parabolic conduction band, or a [[Narrow-gap semiconductor]]. It displays an inverted band structure, and the optical energy gap, e<sub>g</sub>, is less than 0. When deposited by thermal [[evaporation (deposition)]], cadmium arsenide displayed the Schottky ([[thermionic emission]]) and [[Poole–Frenkel effect]] at high electric fields.<ref>{{Cite journal | doi = 10.1016/j.apsusc.2005.12.151| title = Van der Pauw resistivity measurements on evaporated thin films of cadmium arsenide, Cd<sub>3</sub>As<sub>2</sub>| journal = Applied Surface Science| volume = 252| issue = 15| pages = 5508–5511| year = 2006| last1 = Din | first1 = M.| last2 = Gould | first2 = R. D. | bibcode = 2006ApSS..252.5508D}}</ref>

=== Magnetoresistance ===

Cadmium Arsenide shows very strong [[quantum oscillations]] in resistance even at the relatively high temperature of 100K.<ref>{{cite journal |last1=Narayanan |first1=A. |last2=Watson |first2=M. D. |last3=Blake |first3=S. F. |last4=Bruyant |first4=N. |last5=Drigo |first5=L. |last6=Chen |first6=Y. L. |last7=Prabhakaran |first7=D. |last8=Yan |first8=B. |last9=Felser |first9=C. |last10=Kong |first10=T. |last11=Canfield |first11=P. C. |last12=Coldea |first12=A. I. |title=Linear Magnetoresistance Caused by Mobility Fluctuations in -Doped |journal=Physical Review Letters |date=19 March 2015 |volume=114 |issue=11 |page=117201 |doi=10.1103/PhysRevLett.114.117201|pmid=25839304 |arxiv=1412.4105 |s2cid=35607875 }}</ref> This makes it useful for testing cryomagnetic systems as the presence of such a strong signal is a clear indicator of function.