Magnetic and Electrical Characteristics of Nd3+-Doped Lead Molybdato-Tungstate Single Crystals

Abstract

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.

Magnetic and Electrical Characteristics of Nd3+ and Mn2+-Co-doped Calcium Molybdato-Tungstates Single Crystals

“…Also, our research on microcrystalline scheelite-type lead tungstates doped with Pr 3+ and Nd 3+ ions, as well as lead molybdato-tungstates doped with Gd 3+ ions, showed the nonconductive and paramagnetic properties of these doped materials. However, lead molybdato-tungstate single crystals doped with Nd 3+ ions exhibited n-type semiconducting properties in the intrinsic region and a Fermi energy of 0.04 eV (derived from the diffusion component of thermopower), characteristic of shallow donor levels . Summarizing our results on a wide group of scheelite-type materials (micro- or nanopowders) codoped with divalent d-electron metal ions and trivalent rare-earth metal ones, it can be stated that paramagnetism is dominant everywhere, mainly due to the screening of electrons in the 4f subshells of RE 3+ ions.…”

Magnetic and Electrical Properties of CoRE2W2O10 Ceramic Materials

“…Compared to metals, e.g., for pure copper: E F = 7 eV and T F = 8.12 × 10 4 K, and to nonmetallic conductors, e.g., for Cu 1– x Ga x Cr 2 Se 4 single crystals: E F ∼ 0.3 eV and T F ∼ 3 × 10 3 K, the values for ceramics under study are small. However, they are about 3 orders of magnitude higher compared to the E F values for lead molybdate-tungstate single crystals with an admixture of Nd 3+ …”

“…The temperature-independent contribution of the magnetic susceptibility, χ 0 , estimated from the formula − χ T = C 1 − θ T + χ 0 T = b + χ 0 T where b = C 1 − θ / T is the intercept that tends to the Curie constant C as the temperature T tends to infinity and χ 0 is the slope. χ 0 is equal to zero for all samples, which may be the result of compensation of orbital diamagnetism and van Vleck paramagnetism (Figure ).…”

“…It substantially increases with increasing temperature, i.e., in the intrinsic region above 300 K. The S 2 σ value of several pW cm −1 K −2 for the studied ceramics is much lower compared to the nW cm −1 K −2 value for the spinel semiconductors ZnCr 2 Se 4 :Re 30 and to the μW cm −1 K −2 value for nonmetallic spinel conductors, 31 but significantly higher compared to the above-mentioned single crystals, for which the S 2 σ value is of the order of several tens of fW cm −1 K −2 . 24 Summarizing the results of electrical investigations, it can be concluded that the ceramics under study at room temperature are characterized by low electrical conductivity σ ∼ 6.7 × 10 −7 S/m and the value of the energy gap E g ∼ 2.65 eV, i.e., close to the semiconductor−insulator transition. If a large share of ionic bonding is taken into account in such compounds, nonzero electrical conductivity is mainly due to vacancies and structural defects described in the literature, 32−34 and to a lesser extent to the mixed valence band of cations.…”

“…However, they are about 3 orders of magnitude higher compared to the E F values for lead molybdate-tungstate single crystals with an admixture of Nd 3+ . 24 Figure 8b shows the temperature dependence of the power factor S 2 σ. It substantially increases with increasing temperature, i.e., in the intrinsic region above 300 K. The S 2 σ value of several pW cm −1 K −2 for the studied ceramics is much lower compared to the nW cm −1 K −2 value for the spinel semiconductors ZnCr 2 Se 4 :Re 30 and to the μW cm −1 K −2 value for nonmetallic spinel conductors, 31 but significantly higher compared to the above-mentioned single crystals, for which the S 2 σ value is of the order of several tens of fW cm −1 K −2 .…”