Application of a new virtual crystal approach for the study of disordered perovskites

Ramer, Nicholas J.; Rappe, Andrew M.

doi:10.1016/s0022-3697(99)00300-5

Cited by 90 publications

(51 citation statements)

References 19 publications

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“…(1). Interestingly, one sees that E loc has no effect on the phase transition sequence, which is consistent with recent findings that the VCA approach can reproduce some structural properties of PZT [14,17]. Whether or not E loc is included in the total energy, we find a Curie temperature T c that is higher than the experimental value of 640 K [18].…”

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confidence: 91%

Finite-Temperature Properties ofPb(Zr1−xTix)

2000

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A first-principles-derived approach is developed to study finite-temperature properties of Pb(Zr1−xTix)O3 (PZT) solid solutions near the morphotropic phase boundary (MPB). Structural and piezoelectric predictions are in excellent agreement with experimental data and direct firstprinciples results. A low-temperature monoclinic phase is confirmed to exist, and is demonstrated to act as a bridge between the well-known tetragonal and rhombohedral phases delimiting the MPB. A successful explanation for the large piezoelectricity found in PZT ceramics is also provided. High piezoelectric response is experimentally found in ceramics of PZT around the MPB. The origins of this large piezoelectric response are unclear. On the one hand, semi-empirical simulations predict that the large experimental value of the d 33 piezoelectric coefficient results mainly from the large value of d 33 that a single-crystal PZT would exhibit [4]. On the other hand, recent firstprinciples calculations [5,6] have found that the d 33 coefficient of a tetragonal single crystal of Pb(Zr 0.5 Ti 0.5 )O 3 are estimated to be three times smaller than the experimental value obtained for ceramics at low temperature.Furthermore, recent synchrotron x-ray powder diffraction studies have revealed the existence of an unexpected low-temperature monoclinic phase of PZT at x=0.48 [7], which implies that the phase diagram of PZT is more complex than previously thought. This monoclinic phase may act as a second-order transitional bridge between the tetragonal phase, for which the electrical polarization P lies along the pseudo-cubic [001] direction, and the rhombohedral phase, for which P is along the pseudo-cubic [111] direction. If this is indeed the case, the polarization of the monoclinic phase continuously rotates as the composition x decreases in the MPB region [7]. Such a continuous rotation has yet to be observed.Obviously, accurate simulations are needed to understand the properties of perovskite alloys in general, and of PZT in particular. Since the beginning of the present decade, first-principles methods have emerged as a powerful tool for investigating properties of ferroelectric systems theoretically (see [5,6,8,9] and references therein). However, these methods are essentially restricted to the study of the zero-temperature properties of small cells, while accurate and interesting predictions of alloy properties would require calculations on much larger cells at finite temperature. Ideally one desires a computational scheme with the capability of predicting the properties of "real" perovskite alloy systems at finite temperature, with the accuracy of the first-principles methods.The purpose of this letter is to demonstrate that it is possible to develop such a scheme, and to apply it to study the finite-temperature behavior of PZT in the vicinity of the MPB. Remarkably, we find that the existence of an intermediate monoclinic phase emerges naturally from this approach. Moreover, the theory provides a novel and successful explanation for the large ...

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confidence: 91%

Finite-Temperature Properties ofPb(Zr1−xTix)

2000

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“…u i is directly proportional to the electric dipole of that cell); v i are the dimensionless displacement variables of the cell corners and are used to calculate inhomogeneous strain tensor components for each cell i; {η H } is the homogeneous strain tensor, which allows the simulation supercell to vary in size and shape; 45 σ j characterizes the atomic configuration, with σ j = +1 or −1, corresponding to the presence of a Ba or Sr atom, respectively, at the A-lattice site j ; and {η loc } represents the local strain resulting from the difference in ionic size between Ba and Sr atoms, 44 which is relatively large (∼2%). Here, E VCA gathers the energy terms solely involving the local soft mode, strain, and their mutual couplings resulting from the application of the virtual crystal approximation (VCA) 46,47 to model (Ba 0.5 Sr 0.5 )TiO 3 solid solutions. Also, E loc can be thought of as a perturbative term due to the fact that BST systems possess real Ba and Sr atoms on the A-sites rather than virtual, composition-dependent atoms.…”

Section: Discussionmentioning

confidence: 99%

Elastic excitations in BaTiO3single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

et al. 2013

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The dynamic properties of elastic domain walls in BaTiO 3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90• ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and T c at 405 K, we found a good fit of the squared RUS frequency [∼ (C 11 − C 12 )] to a Vogel-Fulcher process with an activation energy of ∼0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO 3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode.

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“…[13], where a different mixing procedures of VCA was used to approximate the disordered PZT. Nevertheless, it should be noted that the structural properties of PZT may be sensitive to the details of the mixing procedure [11,12].…”

Section: Discussion 41 Structural Propertiesmentioning

confidence: 99%

First‐principles study of structural and elastic properties of the tetragonal ferroelectric perovskite Pb(Zr_0.50Ti_0.50)O₃

Márton

Elsässer

2011

Physica Status Solidi (b)

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Structural and elastic properties of Pb(Zr0.50Ti0.50)O3 are determined in the tetragonal ferroelectric phase using first-principles density functional theory in the local-density approximation. Three ordered arrangements of PZT are considered and compared with a homogeneously disordered model of PZT treated in the virtual-crystal approximation. The ground states of some of these model PZT structures are found to be monoclinic; others, including the energetically most stable structure, are tetragonal

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Application of a new virtual crystal approach for the study of disordered perovskites

Cited by 90 publications

References 19 publications

Finite-Temperature Properties ofPb(Zr1−xTix)

Finite-Temperature Properties ofPb(Zr1−xTix)

Elastic excitations in BaTiO3single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

First‐principles study of structural and elastic properties of the tetragonal ferroelectric perovskite Pb(Zr_0.50Ti_0.50)O₃

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Application of a new virtual crystal approach for the study of disordered perovskites

Cited by 90 publications

References 19 publications

Finite-Temperature Properties ofPb(Zr1−xTix)

Finite-Temperature Properties ofPb(Zr1−xTix)

Elastic excitations in BaTiO3single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

First‐principles study of structural and elastic properties of the tetragonal ferroelectric perovskite Pb(Zr0.50Ti0.50)O3

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First‐principles study of structural and elastic properties of the tetragonal ferroelectric perovskite Pb(Zr_0.50Ti_0.50)O₃