Giant energy density nitride dielectrics enabled by a paraelectric-metaparaelectric phase transition

Abstract

Electrostatic dielectric capacitors are foundational to advance the electronics and electric power devices due to their ultrafast charging/discharging capability and high-power density. However, the low energy density limits the potential for next generation devices in terms of miniaturization and integration. We propose a strategy that relies on inducing a field-driven phase transition that we denote paraelectric-metaparaelectric, which yields an ultrahigh energy density in III-nitrides. III-nitride compounds (Al, Sc, B)N with certain cation concentrations possess a nonpolar hexagonal ground phase which could transform into a polar wurtzite phase under a very large electric field, which is denoted as metaparaelectric with nearly null hysteresis P-E loop. This paraelectric-metaparaelectric transition leads to a polarization saturation at large electric field. The corresponding P-E loop displays a giant energy density of 308 J/cm³ with high efficiency nearly 100%. The proposed paraelectric-metaparaelectric phase transition strategy in nitrides opens an avenue to design of next generation high performance dielectrics.

Fig. 1. Schematic diagram of P-E loops of dielectric materials.

a FE, b RFE, c AFE-FE, and d PE-MPE phase transition under electric field. The blue areas represent energy density W. E₀ represents phase transition field. In panel d, the polarization increases linearly and slowly at low electric field; then, the system enters a second linear regime (MPE region) where the polarization grows more quickly, to eventually yield a large saturation polarization that occurs only at large fields.

Fig. 2. Structure for nitride phases.

a WZ, b HE, c BB, d RS, e ZB phase. Sliver spheres represent cation ions (Al, Sc, B), gray spheres represent N ions.

Fig. 3. Stability and phase diagram of (Al, Sc, B)N.

a The formation enthalpy ∆H of (Al, Sc, B)N system as a function of Sc concentration with B concentration of 22%. b Ternary phase diagram of (Al, Sc, B)N system. c Schematic of the total energy as a function of polarization for PE HE′ and ferroelectric FE WZ′ phases as the Sc concentration increases. d The atomic structures for WZ′, HE′, and RS′ phase, which similar to WZ, HE, and RS phase, respectively, with lattice distortions around B ions. The silver, magenta and green spheres represent Al, Sc and B atoms, respectively. The gray spheres represent N atoms. The point A presents the concentration of Al, Sc and B are 25%, 50% and 25%, respectively.

Fig. 4. The P-E loop and energy storage performance of (Al, Sc, B)N.

The P-E loops for (Al, Sc, B)N with Sc concentration of a 59% and b 50% for B concentration y = 13%, 16%, 19%, 22%, 25%. The applied electric field maximum is 6 MV/cm. c The energy density W and efficiency η as a function of B concentration for Sc concentration from 47% to 59%. d The energy density of (Al, Sc, B)N in possible concentration of Sc and B. P represents polarization change under electric filed comparing to the initial structure under zero field. Open and solid symbols indicate the polarization during the charging and discharging processes, respectively.

Fig. 5. PE-FE, RFE and PE-MPE P-E loops and the corresponding atomic structures.

a P-E loops for PE-FE (blue), RFE (green), and PE-MPE (red). Blue and red colors represent the P-E loop for (Al_0.41Sc_0.59)N and (Al_0.28Sc_0.59B_0.13)N, respectively. Green color represents the experimental results of Bi(Mg_0.5Ti_0.5)O₃-SrTiO₃-based RFE films from ref. . The open and solid symbols represent the charging and discharging behaviors, respectively, where the data is from our first-principles calculations or experiment results of ref. . The solid lines represent fittings using Eq. (2). Note some open symbols are overlaid by solid ones. b and c show, respectively, the atomic structures of the (Al_0.41Sc_0.59)N and (Al_0.28Sc_0.59B_0.13)N compounds under electric fields, corresponding to the data shown in panel a. The silver, magenta and green spheres represent Al, Sc and B atoms. The gray spheres represent N atoms.