Dielectric and IR spectroscopy
Changes in spin and lattice dynamics induced by magnetic and structural phase transitions in multiferroic SrMn7O12
Upon cooling, SrMn7O12 undergoes a series of structural and magnetic phase transitions from cubic to rhombohedral symmetry, and to an incommensurately modulated crystal structure, which is connected with charge and orbital ordering of the Mn cations. We report IR, THz, and Raman spectra of SrMn7O12 ceramics reflecting corresponding changes in the phonon selection rules, including new phonons appearing in spin-order-induced ferroelectric phases .
Soft mode driven local ferroelectric transition in lead-based relaxors
Analysis of IR and THz spectra using Bruggeman effective medium approach revealed that the mesoscopic structure of Pb(Mg1/3Nb2/3)O3 and Pb(Mg1/3Ta2/3)O3 consists of dynamic randomly oriented uniaxially anisotropic polar nanoregions with harder transverse optical polar modes in the direction along the local dipoles [1,2].
Wide Range Dielectric and Infrared Spectroscopy of (Nb+In) co-doped rutile ceramics
The dielectric response of ceramics of co-doped rutile Ti1-x(Nb0.5In0.5)xO2 has been measured via a combination of impedance, high-frequency coaxial, THz transmission, and IR reflectivity spectroscopies spanning 15 decades of frequency between 0.1 Hz and 240 THz . It is argued that the colossal dielectric permittivity reported by other authors can be explained by a combination of thin low-conducting grain boundaries and low-conducting depletion near-electrode layers which give rise to thermally activated dielectric relaxations in higher radiofrequency and low-frequency ranges, respectively.
Electric-field-induced transition from incommensurately to commensurately modulated phase
Antiferroelectric-like polarization hysteresis loops in Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30 were explained by electric-field induced structural phase transition from nonpolar incommensurately modulated structure to polar and commensurately modulated phase . This discovery opens new perspective direction of investigation of lead-free materials for possible electric energy storage.
Infrared, terahertz and microwave spectroscopy of the soft and central modes in PMN
Analysis of IR and THz spectra using Bruggeman effective medium approach revealed that the mesoscopic structure of Pb(Mg1/3Nb2/3)O3 (PMN) consists of randomly oriented uniaxially anisotropic polar nanodomains with harder transverse optical polar modes in the direction along the local dipoles.
Can a tensile tensile strained TiO2 thin film be ferroelectric?
A series of papers about discovery of new ferroelectrics using PFM microscopy has recently been published. On the example of strained TiO2 thin films, which exhibit ferroelectric-like hysteresis loops, we have shown that PFM response can come from electrochemical effects like migration of defects.
Broadband dielectric spectroscopy of lead-free relaxor ferroelectrics
Ba(Zr,Ti)O3 (BZT) and Na1/2Bi1/2TiO3 (NBT) have recently become recently the most studied lead-free relaxor materials for their attractive piezoelectric and interesting physical properties.
Ultra-broadband spectroscopy of dielectric-conductor nanocomposites
The ultra-broadband dielectric spectroscopy is particularly useful for studying dielectric–conductor nanocomposites, particularly near the electrical percolation threshold. Theoretically, we have studied the spectra of effective dielectric response of such composites using several models within the effective medium approximation. It was shown that the divergence of the static permittivity at the percolation threshold is caused by a strong dielectric relaxation, which softens on approaching the threshold with changing the composition, passing through the whole frequency range from infrared down to zero [1-3].
Magnetoelectric multiferroics are materials, which exhibit simultaneously magnetic and ferroelectric order. There is theoretically possible to influence magnetic or ferroelectric domains with electric or magnetic fields, respectively, therefore these materials are intensively studied for their promising potential applications in non-volatile memories. Unfortunately, there are only few multiferroics in nature and most of them work only at low temperatures. We suggested to use large mechanical strain in ultrathin films for preparation of new „artificial“ multiferroics.