First-order polarization process as an alternative to antiferroelectricity

Abstract

Antiferroelectrics generate significant interest since their polarization versus electric field (PE) curves show typical double-hysteresis loops appealing for various applications. Unfortunately, antiferroelectrics are rare. In magnetic compounds, magnetization versus magnetic field (M-H) curves can show analogous double hysteresis loops not only in antiferromagnets but also in systems exhibiting field-induced first-order reorientation of the magnetization through a so-called first-order magnetization process. Here, we show that appealing double-hysteresis P-E loops can also appear from an unprecedented first-order polarization process. Focusing on non-polar CaTiO3, which can be turned ferroelectric under tensile strain, we study epitaxial thin films on differently-oriented NdGaO3 substrates using a combination of theoretical and experimental techniques. We uncover that a certain configuration exhibits double-hysteresis P-E loops that we rationalize from a field-induced abrupt rotation of the polarization. Such a first-order polarization process establishes a promising alternative pathway to achieve double hysterisis P-E loops appealing for practical applications.

Figures (18)

• Figure 1: Sketch of atomic configuration and oxygen octahedra orientation of CaTiO$_\mathrm{3}$ films grown on (a) NdGaO$_\mathrm{3}$ (a) (110)$_{\text{o}}$-oriented and (b) (001)$_{\text{o}}$-oriented. Tensile strain imposed by NdGaO$_\mathrm{3}$ (c) (110)$_{\text{o}}$-oriented and (d) (001)$_{\text{o}}$-oriented as well as the resulting dominant polarization orientations.
• Figure 2: Characterisation of the ferroelectric properties of CaTiO$_3$ films. (a) Experimental polarization versus electric field measurement for a 18.2 nm-thick CaTiO$_\mathrm{3}$ film grown on NdGaO$_\mathrm{3}$ (110)$_{\text{o}}$ along $\vec{a}_{\text{pc}}$ and $\vec{b}_{\text{pc}}$ at $T_{exp}$ = 4.2 K in $Pm$ phase. (b) Experimental dielectric constant versus temperature measurement for the same film as panel (a), along $\vec{a}_{\text{pc}}$ and $\vec{b}_{\text{pc}}$, showing a characteristic peak at $T_{c,exp}$ = 110 K signifying the transition from $Pm$ to $P2_1/m$ phase. (c) Second-principles polarization versus electric field curve for CaTiO$_\mathrm{3}$ strained on NdGaO$_\mathrm{3}$ (110)$_{\text{o}}$ along $\vec{a}_{\text{pc}}$ and $\vec{b}_{\text{pc}}$ at $T_{sim}$ = 40 K in $Pm$ phase. (d) Experimental polarization versus electric field measurement for a 17.4 nm-thick CaTiO$_\mathrm{3}$ film deposited on NdGaO$_\mathrm{3}$ (001)$_{\text{o}}$ along $\vec{a}_{\text{o}}$ and $\vec{b}_{\text{o}}$ at $T_{exp}$ = 4.2 K in $Pm$ phase. (e) Experimental dielectric constant versus temperature measurement for the same film as panel (d), along $\vec{a}_{\text{o}}$ and $\vec{b}_{\text{o}}$ showing a characteristic peak at $T_{c,exp}$ = 80 K signifying the transition from $Pm$ ($P2_1nm$-like) to $Pbnm$ phase. (f) Second-principles polarization versus electric field curve for CaTiO$_\mathrm{3}$ strained on NdGaO$_\mathrm{3}$ (001)$_{\text{o}}$ along $\vec{a}_{\text{o}}$ and $\vec{b}_{\text{o}}$ at $T_{sim}$ = 40 K in $Pm$ ($P2_1nm$-like) phase.
• Figure 3: (a) Energy landscape of CaTiO$_\mathrm{3}$ strained on NdGaO$_\mathrm{3}$ (001)$_\mathrm{o}$, shown as a function of the pseudo-cubic polarization components $P_x$ and $P_y$. The grey line marks the lowest-energy path (nudged elastic band) connecting the $P2_1nm$ ground state and the $Pb2_1m$ metastable phase, defining a polar angle $\theta$ that parameterize the polarization rotation along this path. The landscape exhibits a Mexican-hat-like shape (although not perfectly flat). For electric fields applied along $\vec{a}_\mathrm{o}$ (resp. $\vec{b}_\mathrm{o}$), the system exhibits single (resp. double) hysteresis loops. (b) Reorientation of the polarization in CaTiO$_\mathrm{3}$ strained on NdGaO$_\mathrm{3}$ (001)$_\mathrm{o}$ under electric field along $\vec{b}_\mathrm{o}$ at $T{\mathrm{sim}}=40$ K (Fig. \ref{['fig:NGO_001_elec_and_thermal_mes']}(d)), highlighting an abrupt jump associated with a first-order transition. (c) Energy along the same minimum-energy path shown in panel (a), plotted as a function of the rotation angle $\theta$, and its evolution under electric field applied along $\vec{b}_\mathrm{o}$, as fitted with Eq. \ref{['eq:FOPP']}.
• Figure S1: Atomic force microscopy characterisation of the CaTiO$_\mathrm{3}$ thin films, showing smooth surfaces. Multiple samples from each orientation have been studied, however a representative scan of each orientation is shown. (a) CaTiO$_\mathrm{3}$ thin film on NdGaO$_\mathrm{3}$ (110)$\mathrm{_o}$, showing a mean square roughness of 0.26 nm. (b) CaTiO$_\mathrm{3}$ thin film on NdGaO$_\mathrm{3}$ (001)$\mathrm{_o}$, showing a mean square roughness of 0.18 nm.
• Figure S2: Symmetric laboratory x-ray diffraction scans, from which out-of-plane lattice constants and film thickness were determined using InteractiveXRDFit InteractiveXRDFit. For CaTiO$_3$ on NdGaO$_3$ (001)$_{\text{o}}$, we obtain $c_{\text{o}}/2 = 3.793~ \text{\AA}$ and a thickness of 17.4 nm. For CaTiO$_3$ on NdGaO$_3$ (110)$_{\text{o}}$, we obtain $\lvert \vec{a}_{\text{o}} + \vec{b}_{\text{o}} \rvert /2 = 3.798~\text{\AA}$ and a thickness of 18.2 nm.