A set of 61 ion polarizabilities has been derived from the dielectric constants of 129 oxides and 25 fluorides using a least squares refinement technique in conjunction with the Clausius–Mosotti equation. These polarizabilities can be used to estimate mean dielectric constants of ‘‘well‐behaved’’ compounds. They should be particularly useful in calculation of mean dielectric constants of compounds whose dielectric constants have not been determined. They can also be used as a framework for distinguishing unusual dielectric behavior from normal dielectric behavior where deviations can frequently be attributed to piezo‐ or ferroelectricity, conductivity (ionic or electronic), ‘‘rattling’’ or ‘‘compressed’’ cations with correspondingly high or low polarizabilities, or the presence of dipolar impurities. Deviations observed from calculated dielectric constants can be used to search for unusual physical behavior.

Dielectric polarizabilities of ions in oxides and fluorides

An extensive set of infinite-wavelength refractive indices recently derived from a single-oscillator Sellmeier equation [J. Phys. Chem. Ref. Data 31, 931 (2002)] was used to obtain mean total polarizabilities for 340 oxides, 3 hydroxides, 46 oxyhydroxides, 10 oxyfluorides, 8 oxychlorides, 80 hydrates, and 51 fluorides. These data, in conjunction with the polarizability additivity rule and a least-squares procedure, were used to obtain electronic polarizabilities for 79 cations, ${\mathrm{H}}_{2}\mathrm{O}$, and 4 anions $({\mathrm{F}}^{\ensuremath{-}},{\mathrm{Cl}}^{\ensuremath{-}},{\mathrm{OH}}^{\ensuremath{-}},{\mathrm{O}}^{{2}_{\ensuremath{-}}})$. Using literature values for free-cation polarizabilities, neglecting cation coordination, and allowing the variation of anion polarizability according to $\mathrm{log}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\alpha}}_{\ensuremath{-}}=\mathrm{log}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\alpha}}_{\ensuremath{-}}^{o}\ensuremath{-}{N}_{o}∕{V}_{\mathrm{an}}^{2∕3}$ where ${\ensuremath{\alpha}}_{\ensuremath{-}}=$anion polarizability, ${\ensuremath{\alpha}}_{\ensuremath{-}}^{o}=$empirical free-anion polarizability, ${V}_{\mathrm{an}}=$anion molar volume and ${N}_{o}=$a constant, the refinement gives agreement $(\ifmmode\pm\else\textpm\fi{}5%)$ in only 92 out of 381 total mean polarizabilities of 252 compounds. Varying cation polarizabilities, but still neglecting dependencies on cation coordination numbers (CN), allowed us to reproduce total polarizability values to within 5% for 611 out of 650 data on 487 oxides, hydrates, oxyfluorides, and oxychlorides. In the next stage we modified a light-scattering (LS) model by Jemmer et al. [J. Phys. Chem. A 102, 8377 (1998)] to give the expression $\ensuremath{\alpha}(\mathrm{CN},R)=[{a}_{1}+{a}_{2}{\mathrm{CN}}_{\mathrm{ca}}{e}^{\ensuremath{-}{a}_{3}R}{]}^{\ensuremath{-}1}$, where ${\mathrm{CN}}_{\mathrm{ca}}=$the number of nearest-neighbor ions (cation-anion interactions); $R=$cation-anion interatomic distance; and ${a}_{1}$, ${a}_{2}$, and ${a}_{3}$ are constants. This expression provides for a smooth decrease in polarizability at low CN's to the free-cation value at infinite CN's $(R=\ensuremath{\infty})$. Fitting polarizability values for Mg, Ca, Sr, Ba, Pb, Y, and La to this relationship provided a fit to within 5% of 601 out of 650 data. The final step in the refinement process, which used 534 total polarizabilities from 387 compounds, excluded compounds with (1) sterically strained (SS) structures, (2) corner-shared octahedral (CSO) network and chain structures such as perovskites, tungsten bronzes, and titanite-related structures, and (3) piezoelectric (PZ) and/or pyroelectric (PY) structures with abnormally high deviations of observed from total calculated polarizabilities. This final refinement, which provides 79 cation polarizabilities with values for Li, Mg, Ca, Sr, Ba, Pb, B, Al, Ga, Sc, Y, $\mathrm{Lu}\ensuremath{\rightarrow}\mathrm{La}$, Ge, and Ti in varying CN's, shows a standard deviation of 0.150 and no discrepancies $g4%$. Systematic comparisons of differences $(\mathrm{\ensuremath{\Delta}}{Z}^{*})$ of Born effective charges $({Z}^{*})$ from formal valence values with deviations of certain ions in $\ensuremath{\alpha}\text{\ensuremath{-}}{r}^{3}$ plots and with differences between empirical and free-ion $\ensuremath{\alpha}$'s indicate good correlations with metal $d$-oxygen $p$-hybridization and covalence. The level of differences increases in the order alkali ions $\ensuremath{\rightarrow}$ alkaline earth ions $\ensuremath{\rightarrow}$ transition metal ions such as ${\mathrm{Ni}}^{2+},\phantom{\rule{0.3em}{0ex}}{\mathrm{Mn}}^{2+},\phantom{\rule{0.3em}{0ex}}{\mathrm{Cd}}^{2+},\phantom{\rule{0.3em}{0ex}}{\mathrm{Pb}}^{2+},\phantom{\rule{0.3em}{0ex}}{\mathrm{Fe}}^{3+},\phantom{\rule{0.3em}{0ex}}\mathrm{and}\phantom{\rule{0.3em}{0ex}}{\mathrm{Cr}}^{3+}\ensuremath{\rightarrow}\mathbit{M}$ ions found in $A\mathbit{M}{\mathrm{O}}_{3}$ perovskites where $\mathbit{M}={\mathrm{Ti}}^{4+},\phantom{\rule{0.3em}{0ex}}{\mathrm{Zr}}^{4+},{\mathrm{Nb}}^{5+},\phantom{\rule{0.3em}{0ex}}\mathrm{and}\phantom{\rule{0.3em}{0ex}}{\mathrm{Ta}}^{5+}$. We ascribe the differences between our empirical polarizabilities and the free-ion values to charge transfer, effectively increasing cation polarizabilities and decreasing anion polarizabilities. Systematic discrepancies are associated with compounds having SS, CSO, and PZ/PY structures. Underbonded cations such as Mg in ${\mathrm{Mg}}_{3}{\mathrm{Al}}_{2}{\mathrm{Si}}_{3}{\mathrm{O}}_{12}$ (garnet) lead to augmented cation polarizabilities that result in increased observed total calculated polarizabilities (up to 6%). Conversely, overbonded cations in the ${\mathrm{KClO}}_{4}$ structure lead to diminished cation polarizabilities and decreased observed total calculated polarizabilities. Deviations, $\ensuremath{\Delta}$, (up to 10%) of observed from total calculated polarizabilities are found in perovskite compounds such as ${\mathrm{SrTiO}}_{3}$. The octahedral corner-sharing and ${\mathbit{M}}^{\mathbit{n}+}\text{\ensuremath{-}}{\mathrm{O}}^{2\ensuremath{-}}\text{\ensuremath{-}}{\mathbit{M}}^{n+}$ one-dimensional chains lead to enhanced covalency accompanying the $\mathbit{M}\phantom{\rule{0.3em}{0ex}}nd\ensuremath{-}\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ hybridization that, in turn, leads to augmented total polarizabilities and refractive indices. Both $(+)$ and $(\ensuremath{-})$ deviations from additivity in piezoelectric (PZ) and/or pyroelectric (PY) structures are caused by (1) underbonded cations in SS and enhanced $\mathbit{M}\phantom{\rule{0.3em}{0ex}}nd\ensuremath{-}\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ hybridization in CSO compounds, (2) overbonded cations in compounds showing $(\ensuremath{-})$ deviations such as ${\mathrm{NaBe}}_{4}{\mathrm{SbO}}_{7}$, (3) large displacement factors of ${\mathrm{O}}^{2\ensuremath{-}}$ ions in ${\mathrm{KLiSO}}_{4}$ and ${\mathrm{RbLiSO}}_{4}$, and (4) the presence of mobile water molecules in ${\mathrm{Li}}_{2}{\mathrm{SO}}_{4}∙{\mathrm{H}}_{2}\mathrm{O}$.

Empirical electronic polarizabilities in oxides, hydroxides, oxyfluorides, and oxychlorides

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu3+ was detected in the range of 570–650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si4+–Ca2+ to replace Al3+–Y3+, which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu3+ to Eu2+. The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1–xAl1–xSixO4:Eu0.01 (x = 0–0.30) exhibit both green emission of Eu2+ (4f65d1–4f7, broadband around 503 nm) and red-orange emission of Eu3+ (5D0–7F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1–xAl1–xSixO4:Eu0.01 (x = 0–0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, w...

Crystal-Site Engineering Control for the Reduction of Eu3+ to Eu2+ in CaYAlO4: Structure Refinement and Tunable Emission Properties

In the present work, a systematic study on microwave properties of Ca1-xBixMo1-xVxO4 (0.2 ≤ x ≤ 0.5) solid solution ceramics synthesized by using the traditional solid-state reaction method was conducted. A scheelite structured solid solution was formed in the composition range 0.2 ≤ x ≤ 0.5. We successfully prepared a microwave dielectric ceramic Ca0.66Bi0.34Mo0.66V0.34O4 with a temperature coefficient of resonant frequency (TCF) near to zero and a low sintering temperature by using (Bi, V) substituted (Ca, Mo) in CaMoO4 to form a solid solution. The Ca0.66Bi0.34Mo0.66V0.34O4 ceramic can be well sintered at only 870 °C and exhibits good microwave dielectric properties with a permittivity (er) ˜21.9, a Qf ˜18,150 GHz (at 7.2 GHz) (Q = quality factor = 1/dielectric loss; f = resonant frequency), a TCF ˜ + 0.1 ppm/°C. The chemical compatibility with silver indicated that the Ca0.66Bi0.34Mo0.66V0.34O4 ceramic might be a good candidate for the LTCC applications.

Microwave dielectric properties of low firing temperature stable scheelite structured (Ca,Bi)(Mo,V)O4 solid solution ceramics for LTCC applications

Eu3+ and/or Tb3+-doped CaYAlO4 phosphor samples were synthesized by Pechini-type sol–gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. For CaYAlO4:Tb3+, it is shown that the Tb3+-doping concentration has a significant effect on the 5D3/5D4 emission intensity of Tb3+, which is attributed to the cross relaxation from 5D3 to 5D4. Under the 4f8 → 4f75d excitation of Tb3+ or low-voltage electron beams excitation, the CaYAlO4:Tb3+ phosphors show tunable luminescence from blue to cyan, and then to green with the change of Tb3+-doping concentration. The CaYAlO4:Eu3+ samples exhibit a reddish-orange emission of Eu3+ corresponding to 5D0,1 → 7F0,1,2,3 transitions. Furthermore, a white emission can be realized in the single phase CaYAlO4 host by reasonably adjusting the doping concentrations of Tb3+ and Eu3+ under low-voltage electron beams excitation. Compared with the commercial blue (Y2SiO5:Ce3+) and green (ZnO:Zn) phosphors, CaYAlO4:0.1%Tb3+ and CaYAlO4:5%Tb3+ phosphors have higher CL intensity and stability under continuous electron bombardment. Due to the excellent CL properties and good CIE chromaticity coordinates, the as-prepared Tb3+/Eu3+-doped CaYAlO4 nanocrystalline phosphors have potential application in FEDs devices.

Nanocrystalline CaYAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays

Dielectric constants and crystal structures of CaYAlO4, CaNdAlO4, and SrLaAlO4, and deviations from the oxide additivity rule

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Dielectric constants and crystal structures of CaYAlO4, CaNdAlO4, and SrLaAlO4, and deviations from the oxide additivity rule