Rare earth oxide-phosphates (REOPs) form a largely unexplored family of refractory lanthanides and yttrium compounds with general formula RExOy(PO4)z. They are of interest for applications ranging from thermal barrier coatings to catalysts and magnetic materials. At least four REOPs phases were experimentally identified with RE/P ratios from 7:3 to 6:1, however the structures were solved only for 3:1 phases (RE3O3(PO4)). In this work we report the structure for the 7:3 phases (RE7O6(PO4)3) derived by ab initio analysis of models based on previously reported oxide-vanadate analogues. The most stable structures for all 7:3 REOPs were found to be isotypic, adopting monoclinic symmetry with space group P21/c. The structures were validated by comparison of their powder X-ray diffraction patterns to those of synthesized La, Pr, Nd, Sm, Eu, Gd and Tb 7:3 phases (Rietveld refinement for all except Tb). Ab initio analysis of thermodynamic stability showed that all 7:3 REOPs are unstable at 0 K toward decomposition to REPO4 and RE3PO7 or RE2O3. The entropy contribution stabilizes RE7O6(PO4)3 phases for light rare earth elements above 1000 K, however, starting with Dy, computationally predicted stabilization temperature is higher than estimated melting points of RE7O6(PO4)3, which is consistent with observed synthesis pattern.

Rare-earth oxide-phosphates (historically termed oxyphosphates) occupy the compositional space between RE2O3 and REPO4 and form during REPO4 melting and high-temperature degradation of REPO4-based environmental barrier coatings. For several reported stoichiometries, reliable structural models remain unavailable because these phases are low-symmetry, large-unit-cell compounds that seldom form crystals suitable for single-crystal X-ray diffraction. Here, we predict the crystal structure of the compounds reported in the literature as "RE8P2O17" (RE: Sm to Lu, Y) by combining finite-temperature ab initio molecular dynamics (AIMD) simulations with targeted experiments. Syntheses and electron microprobe analysis show the correct RE:P ratio is 3.5, corresponding to RE14P4O31 (14:4). Starting from the melt, AIMD simulations in the SLUSCHI framework, followed by symmetry-constrained relaxation, yield a complex (62 distinct oxygen sites on general positions), monoclinic Pc structure which represents a hitherto unknown structure type. It can be described as a defect fluorite (bixbyite, C-type RE2O3) structure penetrated along one direction by tunnels containing (PO4) tetrahedra. The structure was initially predicted for Y14O15(PO4)4 and was validated for RE = Sm, Eu, Gd, Tb, and Y against synchrotron or laboratory X-ray powder diffraction patterns. Extending the model across the rare-earth series yields consistent lattice trends and places all oxide-phosphates RE14O15(PO4)4 within 46 meV/atom of the 0 K convex hull. A finite-temperature free-energy analysis from MD trajectories predicts entropy stabilization of Y14O15(PO4)4 above ~1,305 K, reconciling metastability at 0 K with observed synthesis and helping resolve discrepancies among published Y2O3-YPO4 phase diagrams.

We report the crystal structure and electric transport and/or dielectric properties of the Ba(PO4)2M2O3 compounds, for M = Ta, Nb as well as the mixtures Ta/Nb, W/ Nb and W/Ta. While the existence of these phases has already been reported in parts, their accurate crystal structures remained unclear but suggest the R-3m space group for M = Ta and Nb. Here the crystal symmetry was revised to the chiral R32 space group, as confirmed by SHG. Furthermore, looking at them from the new viewpoint of the only recently discovered tungsten counterpart (certified R-3m symmetry) opens wide perspectives on materials properties of this family of compounds. For the d0 Nb/Ta5+ phases, we confirm that they are large-gap semiconductors (between 3.7 and 4.8 eV) with weak frequency dependence of the permittivity and low dielectric loss. For mixed Nb/Ta semiconductors the compositional dependence of the bandgap (Eg) and the dielectric constant (E'r) have been analyzed using a bowing parameter and a Clausius-Mosotti law, respectively. For M = Ta, the inversely related Eg and E'r values stand out of the global behavior of the solid solution. The analogy with the M = W case is all the more interesting, since Ba(PO4)2W2O3 is a rare example of a W compound in a single 5+ valence. It constitutes the m = 2 member of the recently-discovered [Ba(PO4)2][WmO3-m] layered-monophosphate bronze series (L-MPTB's). In this subclass, the occurrence of genuine 2D robust metallicity confined in thin areas of their crystal structures validate exotic electronic features hold by the (d0/d1) mixed W5/6+ valence imposed by the stoichiometry. Our work suggests the miscibility of electronically inactive d0 Ta/Nb5+ and d1 W5+ species in an extended compositional phase diagram. The possibility to tune and further confine the electron density of chemically modified L-MPTB is discussed towards intriguing opportunities.

The crystal structures of the low‐temperature (LT) and high‐temperature (HT) modifications of silver pyrophosphate, Ag 4 P 2 O 7 , were determined from single‐crystal X‐ray data. Thermal analysis, vibrational and 31 P‐MAS‐NMR spectroscopy studies, and density functional theory calculations complement the results. The crystal structure of HT‐Ag 4 P 2 O 7 ( T = 487 °C, , Z = 2, a = 5.5734(5) Å, c = 13.7613(18) Å) is very similar to that of the aristotype, γ ‐K 4 P 2 O 7 , whereas the crystal structure of LT‐Ag 4 P 2 O 7 ( T = 25 °C, P 3 1 21/ P 3 2 21, Z = 6, a = 5.5128(1) Å, c = 40.8723(11) Å) differs significantly from LT‐K 4 P 2 O 7 . The experimental results and those of DFT structure optimization yield bent pyrophosphate groups (bridging angle ∠(P−O b −P) ≈ 129°) for both LT‐ and HT‐Ag 4 P 2 O 7 , while their conformations change from eclipsed (HT) to staggered (LT). For one half of the Ag + cations in the HT modification, the unusual ninefold coordination in a truncated hexagonal pyramid changes to a distorted tetrahedral coordination in the LT form. Structural/dynamic instability expresses itself by formation of multinary compounds in the systems A 4 P 2 O 7 /Ag 4 P 2 O 7 ( A = Li, Na). Thus, the crystal structures of Li 3 AgP 2 O 7 and LiAg 3 P 2 O 7 show no similarity at all to that of Ag 4 P 2 O 7 , while the closely related crystal structure of Na 2 Ag 2 P 2 O 7 shows distinct ordering of Na + /Ag + despite similar ionic radii.

The debate in the literature whether the triclinic room-temperature crystal structure of iron(II) pyrophosphate (Fe2P2O7) is centrosymmetric or not has been clearly resolved on the basis of new single-crystal X-ray intensity measurements. This study additionally revealed that Fe2P2O7 undergoes three reversible phase transitions between -140 and 190°C, with the modifications denoted with decreasing temperature as β, α3, α2 and α1. The room-temperature form, α2-Fe2P2O7, indeed crystallizes in a centrosymmetric but incommensurately modulated structure, a fact that has not been recognized for more than 40 years. For better comparison with the C-centred monoclinic thortveitite-type aristotype (space group type C2/m), the structure of the hettotype α2-Fe2P2O7 is described in the superspace group C1(αβγ)0 with a = 6.6393 (6), b = 8.4748 (6), c = 4.4839 (3) Å, α = 90.036 (5), β = 103.962 (7), γ = 92.929 (6)° and a modulation wavevector q = 0.4489 (3)a* + 0.2517 (3)b* + 0.3646 (3)c*. The α2 modification undergoes two phase transitions towards periodic structures. On heating, a triclinic structure described in C1 with very similar lattice parameters is realized above 85°C for the corresponding α3 modification. It can be considered as the non-modulated basic structure of the α2 modification. At about 185°C, α3-Fe2P2O7 transforms to the thortveitite-type β modification, which remains stable up to at least 1000°C. On cooling the α2 modification, a triclinic structure of the low-temperature α1 modification forms below -140°C, which can be considered as a twofold superstructure of the α3 modification with q = ½a* + ½b* + ½c*. The result of these phase transitions from the thortveitite-type β-modification via the triclinic α3 phase and the incommensurately modulated triclinic α2 modification to α1-Fe2P2O7 is the complete ordering of the pyrophosphate anion in the low-temperature phase with a P-O-P bridging angle of 151.91 (8)°. This ordering is accompanied by the lowering of the coordination number of one half of the Fe2+ ions from 6 to 5.

The debate in the literature whether the triclinic room-temperature crystal structure of iron(II) pyrophosphate (Fe 2 P 2 O 7 ) is centrosymmetric or not has been clearly resolved on the basis of new single-crystal X-ray intensity measurements. This study additionally revealed that Fe 2 P 2 O 7 undergoes three reversible phase transitions between −140 and 190°C, with the modifications denoted with decreasing temperature as β, α 3 , α 2 and α 1 . The room-temperature form, α 2 -Fe 2 P 2 O 7 , indeed crystallizes in a centrosymmetric but incommensurately modulated structure, a fact that has not been recognized for more than 40 years. For better comparison with the C -centred monoclinic thortveitite-type aristotype (space group type C 2/ m ), the structure of the hettotype α 2 -Fe 2 P 2 O 7 is described in the superspace group C 1 (αβγ)0 with a = 6.6393 (6), b = 8.4748 (6), c = 4.4839 (3) Å, α = 90.036 (5), β = 103.962 (7), γ = 92.929 (6)° and a modulation wavevector q = 0.4489 (3) a * + 0.2517 (3) b * + 0.3646 (3) c *. The α 2 modification undergoes two phase transitions towards periodic structures. On heating, a triclinic structure described in C 1 with very similar lattice parameters is realized above 85°C for the corresponding α 3 modification. It can be considered as the non-modulated basic structure of the α 2 modification. At about 185°C, α 3 -Fe 2 P 2 O 7 transforms to the thortveitite-type β modification, which remains stable up to at least 1000°C. On cooling the α 2 modification, a triclinic structure of the low-temperature α 1 modification forms below −140°C, which can be considered as a twofold superstructure of the α 3 modification with q = ½ a * + ½ b * + ½ c *. The result of these phase transitions from the thortveitite-type β-modification via the triclinic α 3 phase and the incommensurately modulated triclinic α 2 modification to α 1 -Fe 2 P 2 O 7 is the complete ordering of the pyrophosphate anion in the low-temperature phase with a P—O—P bridging angle of 151.91 (8)°. This ordering is accompanied by the lowering of the coordination number of one half of the Fe 2+ ions from 6 to 5.

Single-phase synthesis of alpha(II)-VOPO4 has been achieved by meticulous control of the seed formation and water vapor. The solid solution (V1-xNbx)OPO4 (0.1 <= x < 1.0) (alpha(II)-VOPO4/MoOPO4-type structure) has been obtained by solution combustion synthesis. It is thermodynamically stable only for x >= 0.8; for smaller x values, equilibration leads to beta-VOPO4 and (V0.2Nb0.8)OPO4. With increasing niobium content, the a-axis of the tetragonal unit cell increases, while the c-axis decreases. Calculated model structures (density functional theory (DFT) using CRYSTAL17, PW1PW hybrid functional, and D3 dispersion correction) suggest that the dopant Nb5+ cations lead to less distorted [(V-V equivalent to O)O4O] octahedra in their vicinity. The experimental vibrational (IR, Raman) and electronic ultraviolet/visible (UV/vis) spectra show considerable variation with composition, perfectly reflecting the calculated dopant effects. These results suggest that within the solid solution [(V-V equivalent to O)O4O] and [(Nb-V equivalent to O)O4O] polyhedra are present as in the boundary phases in addition to just one type of geometrically slightly modified [(V-V equivalent to O)O4O] and [(Nb-V equivalent to O)O4O] groups. The continuous variation of lattice parameters with x is related to the concentration of these four types of polyhedra. Reversible reduction (hydrogen) and reoxidation (air) of (V1-xNbx)OPO4 are possible at 400 degrees C. Thus, ((V0.5Nb0.5V)-Nb-V)OPO4 yields ((V0.5NbV)-Nb-III)O0.5PO4, which decomposes at 800 degrees C in a sealed ampule to (VPO4)-P-III and (NbOPO4)-O-V.

The newly discovered series of layered monophosphate tungsten bronzes (L-MPTB) [Ba(PO4)2]WmO3m-3 consist of m-layer-thick slabs of WO6 octahedra separated by barium-phosphate spacers. They display a 2D metallic behavior confined in the central part of the perovskite slabs. Here, we report the missing m = 2 member of this series, containing the rather uncommon W5+ oxidation state. We have analyzed its structure-property relationships in relation to the other members of the L-MPTB family. In particular, we have determined its crystal structure by means of single-crystal X-ray and electron diffraction and investigated its physical properties from resistivity, Seebeck-coefficient and heat-capacity measurements combined with first-principles calculations. All the L-MPTB compounds show metallic behavior down to 1.8 K without any clear charge-density-wave (CDW) order. The m = 2 member, however, displays an increased influence of the spacer that translates into anisotropic negative thermal expansion, reversed thermopower and reversed crystal-field splitting of the tungsten t2g orbitals. Our analysis of the full [Ba(PO4)2]WmO3m-3 series reveals a systematic and significant W off-centering in their octahedral coordination. We identify the resulting anti-polar character of these W displacements as the crucial aspect behind the 2D metallicity of these systems: It leads to the presence of bound charges whose screening determines the distribution of mobile charges, tending to accumulate at the center of the [WmO3-m] block. We argue that this mechanism is analogous to enhanced conductivity observed for charged domain walls in ferroelectrics, thus providing a general design rule to promote 2D metallicity in layered systems.

AlB4O6N, Al0.97Cr0.03B4O6N, and Al0.83Cr0.17B4O6N are the first representatives of the recently established structure-family of oxonitridoborates containing Al3+. These compounds are isotypic to CrB4O6N and are synthesized in a multi-anvil press under high-pressure/high-temperature conditions of 7.0 GPa/1350 degrees C. Structural refinement by single-crystal X-ray diffraction shows that they crystallize in the space group P6(3)mc (no. 186) with two formula units per cell. Detailed characterization including high-temperature X-ray powder diffraction (HT-XRD), electron probe microanalysis (EPMA), measurements of second harmonic generation (SHG), hardness, photoluminescence properties, vibrational spectroscopy, and band structure calculations reveal intriguing physicochemical properties that strongly resemble the famous material ruby.

The crystal structures of Ti-4(III)[Si2O(PO4)(6)] ( P3 , Z = 3, a = 14.733(1), c = 7.363(1) & Aring;, R1 = 0.040, wR2 = 0.098, 7649 ind. refl., 170 variables), (Fe0.79Ti2.42Ti0.79IV)-Ti-II-Ti-III[Si2O(PO4)(6)] ( P3 , Z = 3, a = 14.6534(2), c = 7.3829(1) & Aring;, R1 = 0.036, wR2 = 0.088, 4026 ind. refl., 171 variables), and (Ti2Ti6IV)-Ti-III(PO4)(6)[Si2O(PO4)(6)] ( R3 , Z = 1, a = 8.446(2), c = 44.21(2) & Aring;, R1 = 0.047, wR2 = 0.120, 1373 ind. refl., 109 variables) have been refined from single-crystal data. The structures show hexagonal closest packing of phosphate groups with metal cations and [Si2O] groups occupying octahedral voids [square(PO4)(6)]. The close relationship of these and other silicophosphate structures to the NiAs and beta-Fe-2(SO4)(3) (see also NaZr2(PO4)(3) "NASICON") structure types is rationalized by group/subgroup considerations. This symmetry approach shows that systematic twinning is highly likely in silicophosphates, thus possibly leading to faulty crystal structure refinements. Our investigation strongly suggests that the proper composition of silicophosphates "(M3P5SiO19)-P-III" (M = Cr, V, Fe, Mo) reported in literature is actually M-4(III)-[Si2O(PO4)(6)]. In the mixed-valent compounds oxidation states were assigned to the cation sites by comparison to Ti2O3, TiP2O7 and FeTiO3. The powder reflectance spectrum of dark-blue (Fe0.79Ti2.42Ti0.79IV)-Ti-II-Ti-III[Si2O(PO4)(6)] shows a strong IVCT transition at nu = 17,500 cm(-1), and magnetic susceptibility data agree very well with the proposed oxidation states.

Blue/turquoise crystals of Sr2CrII(PO4)2 with prismatic shape and edge-length of up to 1 mm were obtained by a vapor-phase moderated solid-state reaction at 1273 K in sealed silica tubes. Its crystal structure was solved and refined from a triply twinned ("trilling") crystal [Pbca (no. 61), Z = 12, a = 10.7064(6) & Aring;, b = 9.2730(5) & Aring;, c = 21.2720(7) & Aring;, R 1 = 0.038]. Sr2Cr(PO4)2 belongs to the small family of inorganic solids containing divalent chromium, where the rare Cr2+ ions are stabilized by the inductive effect of the phosphate groups. As expected from its d 4 (S = 2) electronic configuration, the Jahn-Teller effect (JT) is prominent, leading for the two independent Cr2+ ions to square-pyramidal Cr(1)O4+1 and square-planar Cr(2)O4 coordination within a 3D chromium phosphate network [CrII 2(PO4)4]8. Topologically, the Cr(1) and Cr(2) cations are arranged in separate alternating layers stacked along the c axis. In their respective layers, Cr(1) shows a gapped 2D topology and only weak interaction with the adjacent Cr(2) layers. However, below T N1 similar to 11.3 K, Cr(1) orders antiferromagnetically into a noncollinear structure, leaving nearly paramagnetic Cr(2) idle spins, strongly frustrated by the Cr(1) moments of the next layers. On further cooling, below T N2 similar to 3.6 K, the ordering of Cr(2) occurs via an additional magnetic irreducible representation, which splits the Cr(1) into Cr(1)a and Cr(1)b orbits, thus lifting the frustration on Cr(2). The corresponding P2 1 ca.29.99 magnetic space group forces a crystal symmetry lowering, plausibly signed by a change of the magnetostrictive coefficient from positive to negative below T N2. The optical transitions observed for the JT d 4 ions are in good agreement with our crystal picture from the DFT calculations. A detailed analysis within the angular overlap model explains the surprisingly different d orbital splitting by the ligand field for the chromophores Cr(1)O4+1 and Cr(2)O4.

Multiferroic behavior in the linear-chain spin S = 1/2 compound CuCrO4 was proposed to appear due to competing nearest-and next-nearest-neighbor exchange interactions along the chain. Here, we report on our study of the long-range magnetic ordering using powder neutron diffraction and muon-spin rotation measure-ments. Consistently, both methods find incommensurate long-range antiferromagnetic ordering below 8.5(3) K. We determined the magnetic structure from neutron powder diffraction patterns based on the propagation vector iota = (0, 0, 0.546(1)). At 1.9 K, the magnetic moment of Cu2+ was refined to 0.48(2) mu B. The Cu moments form a helicoidal spiral with an easy plane coinciding with the equatorial planes of the Jahn-Teller elongated CuO6 octahedra. Low-temperature high magnetic field measurements of the magnetization and the dielectric polarization show the multiferroic phase to extend up to similar to 25 T, after which a new, yet unknown phase appears. Full saturation of the magnetic moment is expected to occur at fields much beyond 60 T.

A holistic understanding of the key catalytic features of vanadyl(IV) pyrophosphate enabling high maleic anhydride (MAN) yields in n-butane oxidation has fostered a debate which has continued since the finding of the catalyst. Under reaction conditions, vanadium(V) orthophosphate structure fragments were detected on the surface of the catalyst. However, single-phase alpha II- and beta-VVOPO4 reveal a much lower catalytic performance. This study shows that introducing Nb into alpha II-VOPO4 forming a solid solution (V1-xNbx)OPO4 yields a bulk material with tunable catalytic properties. Selectivities of SMAN = 48% at a conversion of Xn-butane = 30% on (V0.1Nb0.9)OPO4 are shown to be related to the isolation of surface V-sites, which surpass known VOPO4 catalysts by far. A boost in the overall n-butane consumption and MAN selectivity under alkane-rich feed conditions is shown to be another characteristic of (V1-xNbx)OPO4, leading to a highly increased MAN productivity. XPS studies reveal that a progressive replacement of V by Nb induces a reduction of the averaged oxidation state of near-surface V from +4.7 to +4.3, a finding that correlates linearly with an elevated MAN selectivity. This study experimentally confirms site isolation and electronic environment of the near-surface V-species as the key catalytic properties, from which catalyst design rules are derived to optimize partial oxidation reactions.

The hydrogensulfate-sulfates Ln(HSO4)(SO4) (Ln: Sm, Eu, Gd, Tb, Dy) have been crystallized from sulfuric acid and their thermal decomposition behavior has been studied. The crystal structures for all members of the series were refined from X-ray single-crystal diffraction data (for all: Tb(HSO4)(SO4) structure type, P2(1), Z=2, a approximate to 6.66 angstrom, b approximate to 6.63 angstrom, c approximate to 6.82 angstrom, beta approximate to 104.6 degrees). Optical spectra (Sm-Dy) and magnetic susceptibilities (Eu-Dy) have been measured. For comparison the octahydrates Ln(2)(SO4)(3) center dot 8 H2O (Sm, Eu) and the anhydrous sulfates Ln(2)(SO4)(3) (Sm, Eu) have also been characterized by optical spectroscopy and magnetic measurements. Ligand field analyses (angular overlap model) based on these data suggest for the square-antiprismatic [Ln(III)O(8)] chromophores in the hydrogensulfate-sulfates a rather weak ligand field, which is comparable only to that in ultraphosphates LnP(5)O(14) and in contrast to the much stronger field observed for most other lanthanoid(III) oxo-compounds studied so far.

The reactions of ammonium perrhenate and pertechnetate in highly alkaline medium led to the isotypic mixed anionic nitridotrioxidorhenate and -technetate K-3[MO4][MO3N] (M= Tc, Re). Both compounds occur as colorless crystals, which were investigated by single crystal X-ray diffraction. Furthermore, K-3[ReO4][ReO3N] has been studied by means of X-ray photoelectron spectroscopy to determine the oxidation state of rhenium. The obtained results have been complemented by magnetic measurements. IR and Raman spectroscopy indicated the presence of Re-O as well as Re-N bonds.

The Cover Feature shows a 3D view of the single-crystal structure of K3[MO4][MO3N] with M=Tc, Re together with the Raman spectrum of K3[ReO4][ReO3N]. Both compounds were synthesized using a highly alkaline KOH hydroflux. Since single-crystal X-ray diffraction does not prove the presence of nitrogen within the (MO4)-tetrahedra unambiguously, Raman and IR spectroscopy as well as XPS and elemental analysis were conducted. Furthermore, magnetochemical measurements provide evidence for the diamagnetic behavior of the closed-shell heptavalent rhenium species and UV-Vis spectroscopy underpins the absence of mixed valences. The cover was designed by Dr. David van Gerven and Désirée Badea. More information can be found in the Research Article by J. Bruns and co-workers.

Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge-density-wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO4)(2)][WmO3m-3] (m=3, 4 and 5) denominated ' layered monophosphate tungsten bronzes ' (L-MPTB). It results from thick [Ba(PO4)(2)](4-) spacer layers disrupting the cationic metal-oxide 2D units and enforcing an overall trigonal structure. Their symmetries are preserved down to 1.8 K and the compounds show metallic behaviour with no clear anomaly as a function of temperature. However, their electronic structure displays the characteristic Fermi surface of previous bronzes derived from 5d W states with hidden nesting properties. By analogy with previous bronzes, such a Fermi surface should result into CDW order. Evidence of CDW order was only indirectly observed in the low-temperature specific heat, giving an exotic context at the crossover between stable 2D metals and CDW order.

Objectives To evaluate and compare fracture resistance, translucency, and color reproducibility, as well as the effect of aging on the fracture load and color stability of novel monolithic CAD/CAM ceramics. Materials and methods One hundred crowns of uniform thickness were milled from five ceramic blocks ( n = 20): partially crystallized lithium disilicate (PLD) and fully crystallized lithium disilicate (FLD), lithium metasilicate (LMS), 4Y-TZP (SMZ), and 5Y-TZP (UMZ) monolithic zirconia. PLD crowns were glazed, LMS was fired, and FLD was polished. SMZ and UMZ crowns were sintered and polished. Crowns were adhesively cemented to epoxy dies. Half of the crowns ( n = 10) were subjected to 1.200.000 load cycles with thermal cycling. Color space values L, a, b defined by the Commission Internationale de l´Eclairage (CIELAB) were measured before and after aging, and (∆ E ) was calculated. Both aged and non-aged specimens were loaded until fracture in a universal testing machine and the fracture load was recorded. X-ray diffraction (XRD) and scanning electron microscope (SEM) fractographic analysis were carried out on fractured fragments of representative samples. For translucency and color reproducibility, 50 rectangular-shaped specimens were fabricated and processed as described previously. Color values were measured over black and white backgrounds, and the translucency parameter (TP) was computed. Using the shade verification mode, (∆ E ) to shade A3 was calculated. Data were statistically analyzed using one-way and two-way ANOVA, and t -test. Results Aging did not affect fracture resistance significantly ( p > 0.05). The highest mean fracture load was obtained for the SMZ and UMZ. A significant color change was observed after aging in all groups. The highest TP was noted for FLD. SMZ and UMZ had the best shade match. Conclusions Zirconia showed higher fracture resistance and color stability than lithium silicate ceramics. Lithium silicate ceramics were more translucent. The experimental FLD demonstrated high translucency. Clinical relevance Tested ceramics showed sufficient stability to withstand masticatory forces. Characterization of final restorations might be mandatory for better color match.

The mixed-valent, europium borate Eu-5(BO3)(4) was synthesized from Eu2B2O5 and EuB2O4. Its structure was refined by Rietveld analysis. Eu-5(BO3)(4) crystallizes in space group Pnma (a=2229.77(2) pm, b=1599.91(2) pm, and c=877.75(1) pm) and was found to be isostructural with Eu-5(BO2.51N0.49)(4). Powder reflectance spectra (UV/vis/NIR) and magnetic susceptibility data of Eu-5(BO3)(4) and of the reference compounds (EuB4O7)-B-II and (EuBO3)-B-III were measured. The spectrum of the mixed-valent europium(II, III) borate shows the F-7(0)-> F-7(6) transition of the Eu3+ ion and the intervalence charge transfer Eu2+-> Eu3+. The experimental Bohr magneton number of Eu-5(BO3)(4), mu(obs)/mu(B)=14.90, agrees well to mu(calc)/mu(B) for a combination of three Eu2+ and two Eu3+ per formula.