Caloric characteristics of PbTiO3 in the temperature range of the ferroelectric phase transition

The heat capacity and thermal expansion of the PbTiO₃ ceramic sample have been measured in the temperature range 80?C970 K. The electrocaloric and barocaloric efficiencies of lead titanate in the ferroelectric phase transition range have been investigated by analyzing the experimental data in terms of the thermodynamic theory of phase transitions, the electrical equation of state P(T, E), the Pippard equation, and the S(T, p) diagram.     

Effect of Deuteration on Phase Transitions in Vanadium Dioxotetrafluoride

Physics of the Solid State - The crystals of (ND4)3VO2F4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The...     

Structural phase transition in elpasolite-like (NH4)2KWO3F3

A new chemical compound, (NH₄)₂KWO₃F₃, was synthesized. The Rietveld-refined crystal structure was found to be cubic at room temperature and to belong to the elpasolite family (space group ). The heat capacity and unit cell parameters were studied within a broad temperature range. A second-order phase transition was found to occur at 235.4 K and to be well described in terms of phenomenological theory. Hydrostatic pressure broadens the temperature interval of stability of the cubic phase (dT₀/dp = −10.8 K GPa⁻¹). A possible model of structural ordering based on a comparison of the entropy parameters and electron density distribution in oxygen and fluorine atoms is discussed.     

Site‐Selective Occupancy of Eu2+ Toward Blue‐Light‐Excited Red Emission in a Rb3YSi2O7:Eu Phosphor

Establishing an effective design principle in solid‐state materials for a blue‐light‐excited Eu²⁺‐doped red‐emitting oxide‐based phosphors remains one of the significant challenges for white light‐emitting diodes (WLEDs). Selective occupation of Eu²⁺ in inorganic polyhedra with small coordination numbers results in broad‐band red emission as a result of enhanced crystal‐field splitting of 5d levels. Rb₃YSi₂O₇:Eu exhibits a broad emission band at λ_max=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu²⁺ ions preferably occupy RbO₆ and YO₆ polyhedra and show the characteristic red emission band of Eu²⁺. The excellent thermal quenching resistance, high color‐rendering index R_a (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare‐earth phosphors is an effective strategy to target tailored optical performance.     

Physical Properties of a Frustrated Quasi-One-Dimensional NaCuFe2(VO4)3 Magnet and Effect of Chemical Pressure Induced by the Substitution of Sodium for Lithium

Physics of the Solid State - The structural, thermal, static magnetic, and resonance properties of the low-dimensional NaCuFe2(VO4)3 compound obtained by the solid-phase synthesis have been...     

Thermodynamic Properties of Vanadium Oxypentafluoride (IV) (NH4)3VOF5

Physics of the Solid State - The (NH4)3VOF5 crystals have been synthesized and their homogeneity and single-phase structure has been established by the X-ray diffraction, energy dispersive...     

Structure and Thermodynamic Properties of the SmGaGe2O7 Oxide

Physics of the Solid State - The SmGaGe2O7 oxide material has been obtained from initial Sm2O3, Ga2O3, and GeO2 oxides by solid-phase synthesis with annealing in air in the temperature range of...     

Tolerance Factor for Huntite-Family Compounds

Physics of the Solid State - 85 RM3(BO3)4 (R is the rare-earth element (Y, La–Lu) and M = Al, Sc, Cr, Fe, or Ga) compounds with the huntite structure have been analyzed. The analysis of the...     

Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

The dispersion of the relative permittivity ? of a 27-nm-thick epitaxial Fe₃Si iron silicide film has been measured within the E = 1.16–4.96 eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe₃Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe₃Si iron silicide film is formed if the film thickness achieves 5 nm.     

Thermodynamic properties and structure of oxyfluorides Rb<Subscript>2</Subscript>KMoO<Subscript>3</Subscript>F<Subscript>3</Subscript> and K<Subscript>2</Subscript>NaMoO<Subscript>3</Subscript>F<Subscript>3</Subscript>

According to the results of calorimetric and structural studies, the Fm{ie1202-1}m phase in K₂NaMoO₃F₃ remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb₂KMoO₃F₃ samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195 K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds. The barocaloric effect in Rb₂KMoO₃F₃ has been estimated.