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VvanderWaalsforces691●VVVacancies—areonesortofpoint�defectsinsolidswhicharevacant(empty)crystallographicsitesinacrys-tallattice.Thevacancyformationmaybeassociatedwithnumerousfactors,includingthermodynamicpropertiesofacrystalatagiventemperatureandtotalpressure(thermallyactivateddisorder),chemicalequilibrationwithenvironment,intercalationofimpuritiesordopantionsinthelattice(doping-induceddisorder),interfacialprocesses,externalfactorssuchasradiationandelec-tromagneticfields,etc.Thevacancy�diffusionmech-anismisobservedwhen�ionsinthelatticemayjumpbetweenvacantsites.Inthiscase,theion�diffusioncoefficientisproportionaltothevacancyconcentration(seealso�Nernst–Einsteinequation).Asthisprocesscanbevisualizedasvacancymigration,thevacanciesmaybeconsideredasionic�chargecarriers,althoughtherealchargecarriersareions.Important�solidelec-trolyteswiththevacancydiffusionmechanismare�sta-bilizedzirconia,doped�ceriumdioxide,�BIMEVOX,andnumerous�perovskites.Vacantsitesatthecrystal�surfaceandinthenear-surface