A new paper was published on Journal of Materials Science: Materials in Electronics

The paper " New concept of electret-based capacitance, as shown for solder and other conductors " is now available at https://link.springer.com/epdf/10.1007/s10854-022-09366-4?sharing_token=F9d4VqJOZdhH-Evsn_VNc_e4RwlQNchNByi7wbcMAY46C0MZvHc_mOr3DJOJPEdmJlSTj6NfTS092InllZK8Dlnp4X5lM3ZPV11nUFSnocpWTJAjIvat0x3YUJhUY3CT7-ULO4Es0PpMOhclTQX61VIU2C2oRScwn_Myigi3B64=‍

Abstract:

An electret refers to a permanent electric dipole.Nonconductive electrets (polymers and ceramics) have long been studied and utilized,but conductive electrets (metals and carbons) are emerging. This paper introducesthe concept of the electret-based capacitance C’ to elucidate the discharge behavior of conductive electrets inthe form of unpoled solder and other conductors (metals). The C’ is defined as the electret charge Q’ (determined by integrating the dischargecurve) divided by the DC electret voltage V’.   The conventional permittivity-basedcapacitance C (measured) is lowerthan C’ by orders of magnitude.   For Sn-4Ag lead-free solder, C’ (given by Q’/V’) is 620 F, whereas Cis 175 pF.   The electret stems from theinteraction of a small fraction of the carriers (free electrons) with the atoms,as supported by DC polarization asymmetry. For Sn-4Ag, this fraction is 3.5×10^-9. Electret discharge(V’ decreasing to zero) occurs uponshort circuiting.   Self-charge (V’ restored) occurs upon subsequent opencircuiting, being slightly more sluggish than discharge. The electretdischarge/charge amounts to discharge/charge of C’. The discharge/charge time constant is found to approximately equalRC’ (R = resistance) and the discharge/charge energy is found to approximatelyequal ½ C’V’², as expectedfor the discharge/charge of C’ andshown for Sn-4Ag, copper (0% and 37% cold work) and low-carbon steel. Thistwo-fold agreement between theory and experiment for each of the metals studiedstrongly supports the C’ concept. Strongcorrelation occurs among high fraction of carriers that participate, highparticipating charge density and high discharge time constant.