Faculty Directory

Theory of phase transformations and plastic deformation in crystals; theory and modeling of domain structures and their evolution under external fields in functional materials: ferroelectrics, ferromagnetics, ferroelastics and shape memory alloys; theory and modeling of structure and properties of polydomain and heterophase epitaxial films.

Overview

Professor Royburd's research projects include work on:

Theory of Phase Transformations in Solids

• Thermodynamics and structure of heterophase solids
• Elastic domains and polydomain phases
• Martensitic transformations
• Nucleation and growth of crystals in solids
• Phase field approach to crystallization

Theory of Defects and Mechanical Behavior

• Nonconservative movement of dislocations and high temperature mechanical behavior of solids
• Dislocation mechanics of work-hardening
• Structure of grain boundaries and of epitaxial layers
• Pinning of vortexes in type II superconductors

Theory of Domain Structures in Ferroelectrics

• Micro/nanostructures and functional properties of epitaxial films
• Domain structures and properties of graded ferroelectrics

Self-Assembed Nanostructures in Epitaxial Films: Multiferroics

Please refer to the "Publications" tab for the key and recent publications on the theory of elastic domains and its applications cited in the following section.

Elastic Domains: Self-Assembled Micro- and Nanostructures from Steel to Thin Film Multiferroics

The discovery of polydomain phases has been one of the fundamental results of the experimental and theoretical studies of solid phase transformations. Polydomain phases consist of the alternative domains: twins of a product phase or layers of different product phases. These elastic domains minimize the energy of elastic interactions similar to electric and magnetic domains which minimize energy of long range electrostatic and magnetic interactions in ferroelectrics and ferromagnetics. Thermodynamic concept of elastic domains [1] allows us to understand and predict fundamental features of formation of micro- and nanostructure at phase transformations in solids. On this base, the theory of equilibrium polydomain structures including morphology, scale and effect of external fields has been developed for diffusionless transformations martensitic; ferroelastic ferroelectric and ordering [2,3].

Studies of effects of artificial constrains on polydomain structure have led to the theory of adaptive composites consisting of layers of transformable phases constrained by passive layers. It will be shown that unusual thermodynamic properties of adaptive composites including negative elastic modulus at strain controlled deformation and thermodynamic hysteresis at stress controlled deformation can be controlled by change of relative thickness and elastic properties of component layers [4].

Expansion of theory of elastic domains to the epitaxial film [5] has led to intensive experimental and theoretical studies of polydomain structures in shape memory metals, superconductor and ferroelectrics oxide films. The self-assembled structure of non-180° elastic domain with optimum mechanical, electrical, pyroelectrical and piezoelectrical properties had been theoretically designed and experimentally engineered [6,7]. It is shown that under electrical field 180° domains in ferroelectrics can serve as elastic domains too [8]. The cubic elastic domains in ferroelectric constrain nanorods have been predicted recently [9].

The development of the concept of heterophase polydomain structures consisting of domains of different phases [5,10] serves as theoretical background for engineering of self-assembled nanostructures in epitaxial thin films [11-16]. Self-assembled multiferroic nanostructures consisting of ferroelectric and ferromagnetic phases have been modeled and experimentally synthesized. It has been shown that the morphologies can be controlled by changing of constrain conditions through the change of substrate orientations [12-14]. In these structures, the elastic interaction between domains generates the coupling magnetic and electric properties [15,16].

Exploring equilibrium domain structures in non-uniform external field [17,18] and graded crystals [19] have resulted in discovery of domains with wedge morphology. It is suggested that the wedge domain structures should have enhanced sensitivity to external mechanical and electrical field as well to change of temperature.

The idea of wedge domains has been successfully applied to bent nanocrystalline films undergoing the structure transformation to a lower symmetry phase. The elastic interaction between transformed grains results in the self-organization and formation ofpolycrystalline macrodomains. Such kind of wedge macrodomains has been observed in bent film after cubic to tetragonal transformation in BaTiO₃ [20]. This film demonstrates enhanced pyroelectrical effect due to high mobility of macrodomain structures [21].

Professor Roytburd teaches ENMA 461: Thermodynamics of Materials for undergraduate and graduate students. Principal concepts of the thermodynamics which are necessary to understand the thermal properties of materials are discussed in the first part of the course. The statistics-mechanical approach is used to introduce the concepts of entropy, temperature and free energy. A harmonic crystal with point defects and a polymer chain are used as models to formulate basic thermodynamics concepts and the principles. This approach is more effective and better understood by materials engineering students than the traditional approach through the model of an ideal gas. Phase equilibrium and phase transformations in single and multi-component systems are then considered on the basis of the principle minimum free energy. General approach using Landau theory is used to present second order phase transformations in ferroelectrics, ferromagnetics and ferroelastics. The phase diagrams, their construction and applications are considered for several materials. Concluding lectures are devoted to thermodynamics analysis of examples of processing, synthesis and engineering of materials.

The important components of course are more than 50 original problems which serve not only as exercises by also for development of some thermodynamics aspects. A project on experimental measurement of heat capacity is necessary element of the course.

 

Professor Roytburd has published approximately 250 papers. The following are key and recent papers to which he refers in the description of his current research, above.

Please note that some older publications use an alternate spelling of Professor Roytburd's name.

[1] A.L. Roitburd, "Domain structure of crystals formed in a solid phase" Fiz. Tv. Tela, vol.10, p.3619; Soviet Physics-Solid State, 10, 2870, (1968)

[2] A.L. Roitburd, "Martensite transformation as a typical phase transformation in solids", Solid State Physics, 33 (Academic Press, 1978), 317

[3] A.L. Roytburd, "Elastic domains and polydomain phases in solids", Phase Transitions, 45, 1 (1993).

[4] A.L. Roytburd and J. Slutsker, "Deformation of adaptive materials. Part I. Constrained deformation of polydomain crystals"; Part II. Adaptive composite"; Part III: "Deformation of crystals with polytwin product phases", Journal of the Mechanics and Physics of Solids 47 (1999) 2299;2331; 49 (2001) 1795

[5] A.L. Roitburd, "Equilibrim Structure of Epitaxial Layers", Phys. Stat. Sol.(a) 37, 329,(1976)

[6] J. Slutsker, A. Artemev and A.L. Roytburd, "Engineering of elastic domain structures in a constrained layer", Acta Mater., 52, 1731-1742, (2004).

[7] J.Ouyang, J. Slutsker, I. Levin, D.M. Kim, C.B. Eom, R. Ramesh and A.L. Roytburd, "Engineering of Self-Assembled Domain Architectures with Ultra-high Piezoelectric Response in Epitaxial Ferroelectric Films", Adv. Funct. Mater., 17, 2094, (2007)

[8] L. Chen and A.L. Roytburd, "180° ferroelectric domains as elastic domains", Appl. Phys. Lett. 90, 102903, (2007)

[9] J. Slutsker, A. Artemev, A.L. Roytburd, "Phase-field modeling of domain structure of constrain nanoferroelectrics", Physical Review Letters, 100, 087602, (2008)

[10] A.L. Roytburd, "Thermodynamics of polydomain heterostructures. I. Effect of macrostresses, II. Effect of microstresses", J. Appl. Phys. 83(1), 228-245,(1998)

[11] H. Zheng, J. Wang, S.E. Lofland, Z. Ma, L. Mohaddes-Ardabili, T. Zhao, L. Salamanca-Riba, S.R. Shinde, S.B. Ogale, F. Bai, D. Viehland, Y. Jia, D.G. Schlom, M. Wuttig, A. Roytburd, R. Ramesh. "Multiferroic BaTiO₃-CoFe₂O₄ nanostructures", Science, 303, 661-663, (2004)

[12] J. H. Li, I. Levin, J. Slutsker, V. Provenzano, P. K. Schenck, R. Ramesh, J. Ouyang, and A. L. Roytburd, "Self-assembled multiferroic nanostructures in the CoFe₂O₄-PbTiO₃ system", Appl. Phys. Lett., 87, 072909, (2005)

[13] J. Slutsker, I. Levin, J.H. Li, A. Artemev, A.L. Roytburd, "Effect of elastic interactions on the self- assembly of multiferroic nanostructures in epitaxial films" Physical Review B, 73, 184127 (2006)

[14] Igor Levin, Jianhua Li, Julia Slutsker, and Alexander L. Roytburd, "Design of Self-Assembled Multiferroic Nanostructures in Epitaxial Films" Adv. Mat. 18, 2044, (2006)

[15] J. Slutsker and A.L. Roytburd, "Thermodynamics of formation and electro-magnetic coupling of self-assembled multiferroic thin film nanostructures", Phase Transitions, 79, 1083, (2006)

[16] J. Slutsker, Z.Tan, A.L. Roytburd and Igor Levin, "Thermodynamic aspects of epitaxial self-assembly and magnetoelectric response in multiferroic nanostructures", J. Mat. Res. 22(8), 2087, (2007)

[17] A.L. Roitburd, "Instability of Boundary Regions and Formation of Zigzag Interdomain and Interfacial Walls", JETP Lett., 47, 171-174, (1988).

[18] A.L. Roytburd, M. Wuttig and I. Zhukovskiy, "Non-local elasticity of polydomain phases", Scripta Mat. 27(10), (1992)

[19] A.L. Roytburd, J. Slutsker, "Thermodynamics of polydomain ferroelectric bilayers and graded multilayers ", Applied Physics Letters, 89, 042907( 2006).

[20] V. Lyahovitskaya, Y. Feldman, I. Zon, E. Wachtel, I. Lubomirsky, and A. L. Roytburd, "Polycrystalline Macro-Domains Formed by Self-Organization of Ferroelectric Grains", Advanced Materials 17, 1956, 2005.

[21] Y. Yvry, V. Lyahovitskaya, I. Zon, I. Lubomirsky, E. Wachtel and A.L. Roytburd, "Enhanced pyroelectric effect in self-supported films of BaTiO₃ with polycrystalline macrodomains", Appl. Phys. Lett. 90(1), 172905, (2007)