Mechanical characteristics of flux-grown calcium titanate and nickel titanate crystals

Microhardness, fracture mechanism and dielectric behaviour of flux-grown GdFeO3 single crystals

In the present work, different concentrations of Sm 3 + ions doped lithium zinc borate glasses (LBZnFSm: Li 2 CO 3  + H 3 BO 3  + ZnF 2  + Sm 2 O 3 ) were prepared by melt quench technique. Thermal stability, amorphous nature and vibrational modes of lithium zinc borate glasses have been studied by using differential scanning calorimetry, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. Spectroscopic characterization of Sm 3 + -doped lithium zinc borate glasses through absorption, excitation, emission and decay spectra has been carried out. Using absorption spectra nephelauxetic ratios, bonding parameters and energy band gap of the glass were evaluated. Judd–Ofelt (JO) intensity analysis had been performed and JO parameters were estimated for 1.0 mol.% Sm 2 O 3 doped lithium zinc borate glass. Radiative properties such as transition probabilities, branching ratios and radiative lifetime were estimated by using JO parameters. Stimulated emission cross-sections and effective bandwidths of each transition were obtained from the luminescence spectra. The decay curves of Sm 3 + -doped lithium zinc borate glasses exhibit single exponential nature for lower concentrations and gradually changes to non-exponential for higher Sm 3 + concentrations. The experimental life time, quantum efficiency and donor acceptor interaction parameters were also estimated using decay curves of 4 G 5/2 level of Sm 3 + ions in the present glasses. The non-exponential nature of the decay curves has been analyzed by Inokuti–Hirayama model indicating that ion interaction is of dipole–quadrupole nature. Dielectric studies of 0.1, 1.0 and 2.0 mol.% Sm 2 O 3 -doped glasses were undertaken and dielectric constants, Cole–Cole parameters and power-law parameters were also determined.

Spectroscopic and dielectric studies of Sm3 + ions in lithium zinc borate glasses

Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant e?, imaginary part of dielectric constant e?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation.

https://file.scirp.org/pdf/JMP20110100002_92465513.pdf

Impacts of Temperature and Frequency on the Dielectric Properties for Insight into the Nature of the Charge Transports in the Tl2S Layered Single Crystals

The dependence of loss tangent (tan  δ ) and both real and imaginary parts of the dielectric constant ( ɛ ′ and ɛ ″) on temperature in the range 298–923 K and frequency in the range 10 3 –10 6  Hz for flux grown CdTiO 3 single crystals is reported. The ln  σ ac versus T plots suggest the conduction mechanism to be ionic hopping conduction. From ln  σ ac versus frequency curves, it can be seen that the slope decreases with the rise in temperature, suggesting that the ionic hopping conduction diminishes with the rise in temperature. The activation energy at various fixed frequencies is calculated from the slope of the graph between ln  σ ac versus 1/ T (×10 3  K −1 ). Thermal behaviour of flux grown CdTiO 3 crystals using thermoanalytical techniques including TG, DTA and DTG is discussed. Thermal analysis suggests decomposition of CdTiO 3 in the temperature interval of 1386–1693 K leading to the formation of TiO 2 as the final product. Results obtained on application of TG based models viz. Horowitz–Metzger, Coats–Redfern and Piloyan–Novikova are reported. The results of kinetics of thermal decomposition suggest contracting cylinder model as the one that is relevant to the decomposition of CdTiO 3 . The kinetic parameters viz. the order of reaction, activation energy, frequency factor, and entropy of activation using the above mentioned models are computed.

Dielectric properties, ac conductivity and thermal behaviour of flux grown cadmium titanate crystals

Results of dielectric measurements conducted on lanthanum heptamolybdate grown by a gel technique employing the system La(NO 3 ) 3 MoO 3 NH 4 OHHNO 3 Na 2 SiO 3 are presented. The variations of the dielectric constant e′, dielectric loss tan δ and conductivity σ with the temperature and frequency are critically analyzed. The dielectric constant increases with temperature at lower frequencies (10 3 Hz), reaching a maximum value of 320 at 125 °C, after which it abruptly decreases. The dielectric loss tan δ and conductivity σ show both a temperature as well as a frequency dependence. The sharp increase in e′ with temperature is attributed to total polarization resulting from a space charge effect. The functional relationship between the dielectric constant, conductivity and temperature is determined by fitting the observed data with the respective polymeric expressions of the type ϵ ′ = a 0 + a 1 T 2 - lnσ = a + b ( T - T 0 ) 2 The non-linearities and anomalous behaviour of the dielectric constant near the transition temperature, supported by hysteresis studies, indicate the possibility of these materials ferroelectric.

Dielectric studies of lanthanum heptamolybdate crystals grown from gels

The growth of neodymium heptamolybdate crystals is described in the system Nd(NO3)3-MoO3-NH4OH-HNO3- Na2SiO3 using a single gel, single tube technique. The influence of pH, gel concentration and concentration of upper and lower reactants on the size, quality and nucleation density of the crystals is discussed. The techniques of concentration programming and seeded growth are used to enhance the crystal size. Factors influencing the formation of Liesegang rings during the growth are described. Both gel pH and temperature are observed to have a remarkable effect on Liesegang ring formation. The grown crystals are observed to exhibit varied morphology, for example platelets, cuboids, spherulites, crystal aggregates and coalesced crystals.

Growth of neodymium heptamolybdate crystals in silica gels at ambient temperatures

Characterization of lanthanum heptamolybdate crystals grown from silica gels

Thermal behaviour of gel-grown pure and mixed rare earth tartrates of yttrium and samarium is investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal behaviour suggests that the materials are unstable at lower energies and pass through various stages of decomposition, decomposing to respective rare earth oxides which remain stable on further heating. It is estimated that both pure yttrium and pure samarium tartrate crystals carry eight waters of hydration, while mixed yttrium samarium tartrate crystals carry six waters of hydration. Critical examination of TG and DSC curves shows that the initial decompositions are endothermic and the latter are exothermic. Thermal kinetics of these materials has been worked out using Horowitz-Metzger, Piloyan-Novikova and Coats-Redfern equations. Application of these equations to these materials yields values of activation energy, order of reaction and frequency factor which are in reasonably good agreement.

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Thermal behaviour of gel-grown pure and mixed rare earth tartrates of yttrium and samarium

The growth of single crystals of lanthanum heptamolybdate is achieved by allowing controlled diffusion of La ions through silica gel using the system La(NO 3 ) 3 -MoO 3 -NH 4 OH-HNO 3 -Na 2 SiO 3 . The reaction mechanism leading to the growth is reported. Mechanism of crystallization of La heptamolybdate is discussed. Formation of Liesegang rings consisting of La heptamolybdate crystals in the system is reported. It is observed that concentration programming and seeded growth enhances the size of crystals. The crystals grown in the system are single crystal platelets exhibiting squarish or octagonal facets. Some crystals exhibit a spherulitic morphology

Sushma Bhat

Papers

Dielectric studies of lanthanum heptamolybdate crystals grown from gels

Growth of neodymium heptamolybdate crystals in silica gels at ambient temperatures

Characterization of lanthanum heptamolybdate crystals grown from silica gels

Thermal behaviour of gel-grown pure and mixed rare earth tartrates of yttrium and samarium

Growth of lanthanum heptamolybdate crystals by gel technique