Phase diagram and phase transitions in ferroelectrictris-sarcosine calcium chloride and its brominated isomorphs

Abstract

Tris-sarcosine calcium chloride [(TSCC), (CH 3 NHCH 2 COOH) 3 CaCl 2 ] is a uniaxial ferroelectric (FE) with a displacive second-order phase transition near T c = 130 K. A continuous range of solid solutions can be made by substituting Br for Cl, which lowers T c to 0 K at ∼72% Br. Such a quantum critical point differs from that in pseudocubic FEs, such as O-18 SrTiO 3 or doped KTaO 3 . For many years, this system was thought to have only two phases, paraelectric and FE, at ambient pressure. However, we find from dielectric and resonant ultrasound spectroscopy that there are four phase transitions in TSCC and in TSCC:Br (for 0 < Br < 40%): Order-disorder of the sarcosine methyl group at 185 K; displacive FE transition at 130 K (in pure TSCC); a second FE transition [previously hypothesized to be antiferroelectric (AFE) but probably not] at 64 K; and a new anomaly at ∼45 K which might be due to a phase transition or to Debye-like freezing of orientational disorder of some part of the sarcosine molecule. The probable sequence of structures is (upon cooling): Pnma with Z = 4(D 16 2h ) ambient 500 K > T > 185 K, disordered; Pnma with Z = 4(D 16 2h )185 K > T > 130 K (ordered); P n2 1 a with Z = 4(C 9 2v )130 K > T > 64 K (FE); P 2 1 a (C 5 2h ) with Z = 4, 64 K > T > 45 K (not AFE); T < 45 K, unknown structure. A sixth hexagonal structure at high temperatures (>500 K) is hypothesized to be D 3 6h (P6 3 /mcm) with Z = 2, but the samples decompose first at 503 K (230 • C).

Domain wall nanoelectronics

“…This was first described by Bornarel, Lajzerowicz, and Legrand (1974), who found that in such cases ferroelectric polar domain walls could strongly interact with nearby ferroelastic nonpolar walls, tilting both walls and making the nonpolar walls slightly polar. This was recently demonstrated rather spectacularly in ferroelectric tris-sarcosine calcium chloride by Jones et al (2011). Of relevance here is also the fact that ferroelectric domain walls are easily pinned by defects and vacancies, so the switching properties and dielectric contribution of the walls can be modified by manipulating the dopant chemistry.…”

Correlation effects in insulating surface nanostructures

“…16 On the other hand the constrained-GGA results in U = 0.8 eV in case of the Co/CuN system. 7 We also note that a common practice is to use the U and J H as fitting parameters to achieve the best agreement with known experimental data. For instance, the LDA + U method with U = 5.88 eV gives the isotropic exchange interactions between Mn atoms on the CuN surface that agree well with experimental estimates.…”

“…4,6 The next step toward realistic modeling of Mn/CuN, Fe/CuN, and Co/CuN systems would be to take into account the orbital nature of the adatom and hybridization effects between the adatom and surface states. This can be done by using a density functional theory (DFT) method 7 or a many-body Anderson impurity model approach, or their combination. The first-principles DFT-based calculations provide important information concerning ground state properties of the surface nanosystems.…”

“…For instance, the densities of the states obtained for Mn, Fe, and Co/CuN systems by using the local density approximation (LDA), generalized gradient approximation (GGA), and local density approximation taking into account the on-site Coulomb interaction (LDA + U ) demonstrated that the one-particle excitation picture depends on the symmetry of the particular 3d orbital of the adatom. 7 On the other hand for the simulation of the electronic or magnetic excitations in a surface nanosystem, the Anderson model approach seems to be the most natural choice. The parameters for this model can be estimated by using the first-principles calculations.…”

Ferrielectricity in the metal-organic ferroelectric tris-sarcosine calcium chloride

“…TSCC (tris-sarcosine calcium chloride) has a second-order displacive paraelectric (PE) to ferroelectric (FE) phase transition near T c = 130 K. 1,2 Early work by Bornarel and Schmidt 3 showed that trissarcosine calcium chloride also has a structural phase transition at ca. 700 MPa hydrostatic pressure at T=293 K and that the phase boundary extrapolates to << 40K at atmospheric pressure (their studies were limited to T > 77 K).…”