Two-dimensional photonic and phononic crystals based on lithium niobate

Specific features of the preparation and application of photonic and phononic crystals containing two-dimensional periodic domain structures are considered. Particular attention is given to the formation of two-dimensional periodic domain structures in oxide ferroelectrics using strongly focused laser beams. Specific features of the nonlinear properties of such two-dimensional structures during the propagation of optical and acoustic beams through them are described.     

High-frequency ultrasonic studies of the structural phase transition in an La<Subscript>0.875</Subscript>Sr<Subscript>0.125</Subscript>MnO<Subscript>3</Subscript> single crystal

The specific features of a phase transition from a disordered orbital state to an ordered orbital state in an La_0.875Sr_0.125MnO₃ single crystal are investigated using acoustic methods at a frequency f = 500 MHz. The phase transition is accompanied by a distortion of MnO₆ octahedra due to the cooperative Jahn-Teller effect and is a first-order phase transition, as judged from the sharp change observed in the damping of acoustic pulses, the acoustic wave velocity, and the temperature hysteresis. It is revealed that the parameters of the acoustic waves change significantly throughout the temperature range of existence of the cooperatively distorted structure. In an external magnetic field, the structural phase transition is shifted toward lower temperatures.     

Effect of Jahn-Teller distortions on the structural and magnetic ordering in perovskite-type transition-metal oxides

The effect of local and cooperative distortions of oxygen octahedra containing Jahn-Teller ions on the elastic, electric, magnetic, and optical properties of lightly doped lanthanum strontium manganites and irondoped lithium niobate ferroelectric has been experimentally investigated. The formation of nano-and microscale clusters and domains around, respectively, Mn³⁺ and Fe²⁺ Jahn-Teller ions at phase transitions and in magnetic or electric fields were studied. A model is proposed to consistently explain the results of the investigations of Jahn-Teller ions in magnetic and/or electrically ordered materials.     

Formation of submicron partially ordered domain structures in ferroelectric and magnetic materials

Formation of domains and partially ordered periodic domain structures in ferroelectric and magnetic oxides of metals of transition groups has been investigated. Physical features of appearance of submicron periodic domain structures and possibilities of their use for the control over the parameters of high-frequency acoustic waves have been considered using the example of single crystals of lithium niobate and lanthanum-strontium manganites.     

Effect of impurity iron ions on the formation of photoinduced lattices and domain structures in lithium niobate

Processes and mechanisms of the formation of lattices and periodic domain structures in iron-doped lithium niobate monocrystals under the effect of laser beams are examined. The role of Jahn-Teller Fe²⁺ ions in the formation of photoinduced periodic structures is demonstrated.     

Influence of the Jahn-Teller effect on the structural, magnetic, and electrical properties of lightly doped manganites

Features of the structural, magnetic and electric properties in lightly doped La_1?x Sr _x MnO₃ (0.12 < x < 0.18) manganites are studied. Agreement between the types of orbital ordering and the local cooperative Jahn-Teller distortion octahedra is established. The interaction between the Jahn-Teller effect and magnetic ordering is described.     

Dynamics of photo-induced changes in the elastic characteristics of lithium niobate crystals doped with Jahn–Teller Fe<Superscript>2+</Superscript> ions

The effect of admixture Jahn–Teller Fe²⁺ ions on the elastic characteristics of lithium niobate was studied. The appearance of photostrains and a change in elastic moduli under the influence of laser radiation was established, thus enabling the creation of device elements with optically controlled elastic characteristics.     

Transformation of the acoustic mode near the structural and magnetic phase transitions in La1–xSrxMnO3 (x = 0.175) crystal

The peculiarities of the phase transitions in La_0.825Sr_0.175MnO₃ single crystal have been investigated by acoustic methods at the frequency f = 770 MHz. Generation of a magnetoelastic wave near the phase transition at 305 K is revealed, which is assigned to quasi-transverse modes. The most likely cause of the phase transition near T = 305 K and the formation of the quasi-transverse mode is the suppression of local Jahn-Teller distortions.     

Low-temperature electrical conductivity of congruent lithium niobate crystals

The electrical conductivity of lithium niobate crystals was investigated at temperatures between 80 and 450 K as a function of the oxidation-reduction annealing conditions. The results are interpreted in terms of polaron electrical conductivity at room temperature and above. A reduction in the measurement temperature leads to “freezing out” of small-radius polarons, and hopping of Heitler-London bipolarons via unfilled Nb_Li sites becomes the main mechanism responsible for the electrical conductivity. Fiz. Tverd. Tela (St. Petersburg) 40, 1307–1309 (July 1998)