Phase transition(s) in titanite CaTiSiO5: An infrared spectroscopic, dielectric response and heat capacity study

2014

Advances in Physics

111

Domain boundaries typically constitute only a minute fraction of the total volume of a crystal. However, a special (but not unusual) situation can occur in which the domain boundary energy becomes very small. Specifically, the domain size is miniaturized to near-atomic scales and the domain boundary density becomes extremely high. In such cases, the properties of the crystal become dominated by a combination of both the domains and the domain boundaries. This phenomenon differs from most ferromagnetic or ferroelectric materials wherein the motion of the domain boundaries dominates the response. As reported herein, novel emergent phenomena that differ from the properties of either the domains or the domain boundaries may be expected. In this article, we focus on one specific state found in ferroic materials -namely, the adaptive ferroic state. This state can be found, for example, in tweed-like structures in morphotropic phase boundary piezoelectric crystals, ferromagnetic shape memory alloys, and pre-martensitic states. In these materials, the properties of the twin boundaries represent the principal contributors to the functionality of a given system. In fact, further investigations of domain boundary-dominated phenomena could result in novel potential for tailoring functional properties for a desired outcome. It should also be noted that new properties can be designed into twin boundaries that are not the properties of the domains. In this paper, adaptive structures and functional twin boundaries are reviewed, and examples of various observed functionalities (e.g. superconductivity, polarity, and ferroelectricity) and corresponding twin boundary structures are provided. In addition, this review confirms that various theoretically predicted, structurally bridging low-symmetry phases do, in fact, exist. Moreover, the values of the lattice constants of the adaptive state are adjustable parameters that are determined by combinations of cubic, rhombohedral/tetragonal phases, and geometrical invariant conditions. Finally, we show that, in such cases, macroscopic properties are controlled by the unique functionality of the twin walls. Looking forward, domain boundary-dominated phenomena offer an important approach for enhancing the properties of the bulk, and to unique local properties where the "twin is the device". We encourage the community to rethink their approaches to materials by design that have treated the structure as homogeneous and to consider the alternative paradigm where the local structure is different from the apparent average symmetry. PACS: 77 Dielectrics piezoelectrics and ferroelectrics; 64 Equations of state, phase equilibria, and phase transitions; 73 Electronic structure and electrical properties of surfaces, interfaces, thin films, and lowdimensional structures

Section: Order Parameter Couplingmentioning

confidence: 98%

Domain boundary-dominated systems: adaptive structures and functional twin boundaries

Viehland

2014

Advances in Physics

111

“…[45]). Phase fronts occur typically for first-order phase transitions as in martensites and stepwise transitions in ferroelastics [46][47][48][49][50][51]. In second-order transitions, the propagation of phase fronts can be related to defect fields.…”

Section: Front Propagation In Order/disorder Systems With Partially Cmentioning

confidence: 99%

“…Salje a direct consequence of the (partial) order parameter conservation (or of higher-order gradient terms), we find that the pattern formation may well result in real systems from the local conservation of the order parameter [71][72][73] or, what may be termed short-and longrange order of the state parameter [74]. This may also be a way forward for the explanation of the systematic formation of zebra-pattern in optical devices, tweed in superconducting YBaCuO, microstructures in titanite or may be even the reason why chemical modification in radiation damaged materials such as zircon is s direct consequence of the conservation law during the chemical exchange [75][76][77][78][79][80][81][82][83][84][85]. …”

mentioning

confidence: 96%

On the dynamics of ferroelastic domain boundaries under thermal and elastic forcing

2010

Phase Transitions

Self Cite

Experimental observations and some theoretical models for the propagation of ferroelastic domain boundaries and phase fronts are reviewed. While the static configurations of domains and domain walls are reasonably well understood in ferroelastics (and specifically in shape memory alloys), one finds that the dynamic features have been less thoroughly investigated. In most cases, a smooth movement of domain walls in the ballistic limit is observed, accelerated propagation seems not to exist in the time and space limits of most experiments. Pattern formation occurs when the local order parameter is conserved over a length scale which is different from the ferroelastic correlation length. Currently, only few spiky elastic measurements and domain wall jamming in ferroelastics have been reported. Emphasis is given to disordered systems in which the occurrence of 'jerky elasticity' can be expected.

“…Zircon shows two percolation transitions as a result of radiation damage (Salje et al 1999). Titanite in addition undergoes structural transitions between the crystalline phases α, β, and γ (Salje et al 1993;Zhang et al 1995Zhang et al , 1997Chrosch et al 1997;Meyer et al 1996;Hayward et al 2000). These transitions are a consequence of the inherent structural instabilities of the titanite crystal structure.…”

Section: Introductionmentioning

confidence: 98%

“…The orientations of the offcenter dipole vectors are nearly parallel within an individual TiO 6 chain but in opposite directions between neighboring chains. The phase transition between the α phase and the β phase occurs at 496 K. This phase transition has been thoroughly investigated (Speer and Gibbs 1976;Taylor and Brown 1976;Higgins and Ribbe 1976;Oberti et al 1991;Bismayer et al 1992;Salje et al 1993;Zhang et al 1995;Chrosch et al 1997), and is mainly related to a change in the position of the Ti atoms within the octahedron. The average symmetry of the β phase is described by the space group A2/a (C2/c).…”

Section: Introductionmentioning

confidence: 98%

Elastic softening of metamict titanite CaTiSiO5: Radiation damage and annealing

Safarik

Lashley

et al. 2011

American Mineralogist

Self Cite

We have measured the elastic response of radiation-damaged titanite, CaTiSiO 5 , as a function of thermal annealing. We estimate the bulk modulus of the damaged samples (∼24% amorphous) to be 85 GPa, which is much softer than for undamaged crystalline titanite [131.4 GPa;Angel et al. (1999)]. Conversely, the lowest shear modulus of the radiation-damaged material is 52-58 GPa, which is harder that of the undamaged titanite, 46-52 GPa. The bulk and shear moduli of the radiation-damaged materials are close to those of thermal titanite glass, B glass ≈ 75 GPa and G glass ≈ 47 GPa, and are much smaller than expected based on other radiation-damaged materials such as zircon (ZrSiO 4 ). Surprisingly, annealing of the damaged titanite in the range 600 < T < 1000 K leads to additional massive softening of the shear moduli. During annealing the shear modulus of titanite sample 1 softened from 58 to 29 GPa, and sample 2 softened from 52 to 19 GPa. The temperature range for the softening coincides with that found for crystallization of the amorphous regions, as measured previously by diffraction and spectroscopic methods. In contrast to the huge softening of the ultrasonically measured shear modulus, the calorimetrically measured Debye temperature θ D increases by ∼5%, suggesting a small intrinsic hardening of the acoustic shear modes. Additional heating to 1473 K leads, in one titanite sample, to a steep increase of the shear modulus to values much larger than that of the initial, radiation-damaged material. Theoretical models are discussed to rationalize the massive softening due to both radiation damage and subsequent anneal.