9 research outputs found
Electrical and optical properties of new Pr3+-doped PbWO4 ceramics
Polycrystalline samples of new scheelite-type tungstates, Pb1 3x xPr2xWO4 with 0.0098 6 x 6 0.20, where denotes
cationic vacancies have been successfully prepared by a high-temperature solid-state reaction method using Pr2(WO4)3 and
PbWO4 as the starting reactants. The influence of the Pr3+ substitution in the scheelite framework on the structure and optical
properties of prepared new ceramic materials has been examined using powder X-ray diffraction method (XRD) and
UV-Vis-NIR spectroscopy. The results of dielectric studies of Pb1 3x xPr2xWO4 samples showed both low values of dielectric
constant (below 14) and loss tangent (below 0.2). The electrical conductivity and thermoelectric power measurements revealed
a low conductivity ( 2 × 109 S/m) and the sign change of thermoelectric power around the temperature of 366 K
suggesting the p-n transition. These results are discussed in the context of vacancy, acceptor and donor levels as well as
the Maxwell-Wagner model
Effect of Gd3+ substitution on thermoelectric power factor of paramagnetic Co2+-doped calcium molybdato-tungstates
A series of Co2+-doped and Gd3+-co-doped calcium molybdato-tungstates, i.e., Ca13xyCoy
xGd2x(MoO4)13x(WO4)3x (CCGMWO), where 0 < x 0.2, y = 0.02 and represents vacancy, were
successfully synthesized by high-temperature solid-state reaction method. XRD studies and diffuse
reflectance UV–vis spectral analysis confirmed the formation of single, tetragonal scheelite-type
phases with space group I41/a and a direct optical band gap above 3.5 eV. Magnetic and electrical
measurements showed insulating behavior with n-type residual electrical conductivity, an almost
perfect paramagnetic state with weak short-range ferromagnetic interactions, as well as an increase
of spin contribution to the magnetic moment and an increase in the power factor with increasing
gadolinium ions in the sample. Broadband dielectric spectroscopy measurements and dielectric
analysis in the frequency representation showed a relatively high value of dielectric permittivity at
low frequencies, characteristic of a space charge polarization and small values of both permittivity
and loss tangent at higher frequencies
New Gd3+ and Mn2+-Co-Doped Scheelite-Type Ceramics—Their Structural, Optical and Magnetic Properties
New Gd3+- and Mn2+-co-doped calcium molybdato-tungstates with the chemical formula of Ca1−3x−yMny▯xGd2x(MoO4)1−3x(WO4)3x (labeled later as CaMnGdMoWO), where ▯ denotes vacant sites in the crystal lattice, 0 < x ≤ 0.2500 and y = 0.0200 as well as 0 < y ≤ 0.0667 and x = 0.1667 were successfully synthesized by high-temperature solid-state reaction method and combustion route. Obtained ceramic materials crystallize in scheelite-type structure with space group I41/a. Morphological features and grain sizes of powders under study were investigated by SEM technique. Spectroscopic studies within the UV-vis spectral range were carried out to estimate the direct band gap (Eg) and Urbach energy (EU) of obtained powders. EPR studies confirmed the existence of two types of magnetic objects, i.e., Mn2+ and Gd3+ ions, and significant antiferromagnetic (AFM) interactions among them
Efektywność estymacji parametrów funkcji Törnqvista
Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę
Magnetic and Electrical Characteristics of Nd<sup>3+</sup>-Doped Lead Molybdato-Tungstate Single Crystals
Single crystals of Pb1−3x▯xNd2x(MoO4)1−3x(WO4)3x (PNMWO) with scheelite-type structure, where ▯ denotes cationic vacancies, have been successfully grown by the Czochralski method in air and under 1 MPa. This paper presents the results of structural, optical, magnetic and electrical, as well as the broadband dielectric spectroscopy measurements of PNMWO single crystals. Research has shown that replacing diamagnetic Pb2+ ions with paramagnetic Nd3+ ones, with a content not exceeding 0.01 and possessing a screened 4f-shell, revealed a significant effect of orbital diamagnetism and Van Vleck’s paramagnetism, n-type electrical conductivity with an activation energy of 0.7 eV in the intrinsic area, a strong increase of the power factor above room temperature for a crystal with x = 0.005, constant dielectric value (~30) and loss tangent (~0.01) up to room temperature. The Fermi energy (~0.04 eV) and the Fermi temperature (~500 K) determined from the diffusion component of thermopower showed shallow donor levels