High-κ dielectrics for insulating layers are a current key ingredient of microelectronics. X2O3 sesquioxide compounds are among the candidates. Here we show for a typical material of this class, Sc2O3, that the relatively modest dielectric constant of its crystalline phase is enhanced in the amorphous phase by over 40 % (from ∼15 to ∼22). This is due to the disorder-induced activation of low frequency cation-related modes which are inactive or inefficient in the crystal, and by the conservation of effective dynamical charges (a measure of atomic polarizability). The analysis employs density-functional energy-force and perturbation-theory calculations of the dielectric response of amorphous samples generated by pair-potential molecular dynamics.PACS numbers: 77. 22-d,63.20-e,78.30-j,61.66-f High-dielectric constant ("high-κ") materials are gradually replacing silica [1] as gate dielectrics in integrated electronics. Policrystalline layers thereof usually behave badly in electrical terms due to grain-boundary conduction, so that amorphous layers are seriously studied as well. Whether or not the κ of the crystal will be conserved upon amorphization is not obvious a priori [2], and should be assessed during the validation of a candidate dielectric to be used in thin insulating coatings.Considerable attention has been devoted recently [3, 4] to sesquioxides X 2 O 3 with the trivalent cation X=Y, Sc, or a rare-earth atom. Almost all these materials adopt the cubic bixbyite crystal structure. Experiments [3,4] and theory [4,5] largely agree that their static dielectric constant in that phase is in the order of 12 to 15, and of vibrational origin for about ∼60-70%. The microscopic rationale for this behavior was given recently by the present authors [4,5]: the infra-red (IR) active vibrational modes are relatively high-frequency and essentially cation-independent motions.As we discussed in detail elsewhere [2,6,7,8], the dielectric constant κ s =κ ∞ +κ ion in high-κ materials is generally dominated by the lattice-vibrational component κ ion , a factor 2 to 10 larger than the electronic κ ∞ . By its definition(with z the mode charge vector, Ω the system volume, Z * i,α,β the effective or dynamical or Born charge tensor and M i the mass of atom i, ξ i,λβ and ω the eigenvector and eigenfrequency of mode λ at zero wave-vector, and α, β cartesian indexes), a large κ ion is due to large effective polarizabilities as measured by dynamical charges, termed "anomalous" if they exceed nominal ionicity, and to soft IR vibrational modes. A question that naturally arises is, will amorphization, i.e. microscopic disorder, deteriorate the dielectric constant of these oxides ? In this Letter we show, based on ab initio calculations, that scandia, Sc 2 O 3 , has a larger dielectric constant in its amorphous phase than in its crystal phase. This dielectric constant boost is due to a) hardly any loss in dynamical polarizability, and b) disorder-induced IR activation of non-polar low-energy modes related to cation-oxygen combined motions...