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BaSO4, orthorhombic, Pnma (no. 62), a = 8.8806(8) Å, b = 5.4539(5) Å, c = 7.1570(7) Å, V = 346.64(6) Å3, Z = 4, Rgt (F 2) = 0.0141, wRref (F 2) = 0.0329, T = 293 K.

The metal-rich phosphide TaCrP forms from the elements by step-wise solid state reaction in an alumina crucible (maximum annealing temperature 1180 K). TaCrP is trimorphic. The structural data of the hexagonal ZrNiAl high-temperature phase (space group P 6 ‾ 2 m $P\overline{6}2m$ ) was deduced from a Rietveld refinement. At room temperature TaCrP crystallizes with the TiNiSi type (Pnma, a = 623.86(5), b = 349.12(3), c = 736.78(6) pm, wR = 0.0419, 401 F 2 values, 20 variables) and shows a Peierls type transition below ca. 280 K to the monoclinic low-temperature modification (P121/c1, a = 630.09(3), b = 740.3(4), c = 928.94(4) pm, β = 132.589(5)°, wR = 0.0580, 1378 F 2 values, 57 variables). The latter phase transition is driven by pairwise Cr–Cr bond formation out of an equidistant chain in o-TaCrP. The phase transition was monitored via different analytical tools: differential scanning calorimetry, powder synchrotron X-ray diffraction, magnetic susceptibility measurements and 31P solid state NMR spectroscopy.

On Bjørnøya, the exhumed crest of the Stappen High, the lower Permian (Cisuralian) Hambergfjellet Formation represents the only exposed part of the Bjarmeland Group carbonate platform, which occurs widely elsewhere in the subsurface of the Barents Shelf. A complex stratigraphic architecture has earlier been noted for the Hambergfjellet Formation and thickness estimates range from c. 50 to more than 100 m. Moreover, the unit lacks a formal type section, which hampers accurate regional correlations and comparisons. In this stratigraphic study, we integrate new field observations and microfacies analysis with data from previous work to present a composite section which is proposed as the type section for the Hambergfjellet Formation. Four internal units are recognized. Units A and B (post ?late Asselian–?Sakmarian), which consist of mixed carbonate and siliciclastic rocks interpreted to be of shallow marine origin, are restricted to a series of fault-bounded basins defined by gently rotated basement fault blocks. Locally, units A and B onlap or truncate lowermost Permian strata and appear to transgressively fill in antecedent topography presumably created during Sakmarian uplift and erosion of the Stappen High. The distorted character of unit A suggests that slumping was an important process during the initial phase of infilling, amid or soon after transgression. Unit C (?Sakmarian–?early Artinskian) is a thick-bedded, sheet-like limestone unit which contains fauna elements consistent with deposition on a warm-water carbonate platform occasionally subject to subaerial exposure. Unit D (late Artinskian) is a brachiopod-dominated, fusulinid-bearing, bioclastic limestone unit deposited on a fully marine, transitional warm-temperate to cool-water carbonate platform which developed during a late Artinskian circum-Arctic transgression. The unit only occurs in the eastern part of the outcrop belt on southern Bjørnøya due to fault-controlled tilting and peneplanation prior to deposition of the Miseryfjellet Formation (Kungurian–Wordian) limestones. Distinct evidence, including breccia pipes, points to prolonged exposure and karstification of the Hambergfjellet Formation carbonate platform prior to transgression and submergence of the Stappen High in the middle to late Permian (Guadalupian). The presence of angular and highly diachronous unconformities at the base and top of the formation, a series of small grabens, internal dip variations, as well as a conspicuous north to north-eastward thinning manifest tectonism pre-dating the late Permian extensional event along the western Barents Shelf margin. As such, we shed a new light on the Permian tectonostratigraphic evolution of the Stappen High.

The equiatomic metal-rich phosphide NbCrP shows a structural phase transition around 125 K. The structures of the high- and low-temperature modifications were refined from single crystal X-ray diffractometer data of an un-twinned crystal: TiNiSi type, Pnma, a = 619.80(2), b = 353.74(4), c = 735.24(6) pm, wR = 0.0706, 288 F 2 values, 20 variables at 240 K and P121/c1, a = 630.59(3), b = 739.64(4), c = 933.09(5) pm, β = 132.491(6)°, wR = 0.0531, 1007 F 2 values, 57 variables at 90 K. The structural phase transition is of a classical Peierls type. The equidistant chromium chain in HT-NbCrP (353.7 pm Cr–Cr) splits pairwise into shorter (315.2 pm) and longer (373.2 pm) Cr–Cr distances. This goes along with a strengthening of Cr–P bonding. The superstructure formation is discussed on the basis of a group–subgroup scheme. Electronic structure calculations show a lifting of band degeneracy. Protection of the non-symmorphic symmetry of space group Pnma is crucial for the phase transition. The estimated charge modulation is consistent with the interpretation as Peierls transition.

Linarite, PbCuSO4(OH)2, crystallizes as secondary mineral in form of clusters of crystals in Mine du Pradet at Cap Garonne in France. A tiny single crystal was isolated and its structure was refined from synchrotron diffraction data (λ = 0.049592 nm): P121/m1, a = 467.75(2), b = 563.48(4), c = 967.64(5) pm, β = 102.647(5)°, wR = 0.0544, 819 F 2 values and 56 variables. The proton positions were also refined. The Cu2+ cations are located within Cu(OH)2 ribbons and exhibit pronounced Jahn-Teller distortion (d(Cu–O): 2 × 191.9, 2 × 197.3 and 2 × 252.8 pm). The Cu(OH)2 ribbons are condensed with the sulfate tetrahedra and the lead cations. The latter are coordinated to eight oxygen atoms in a slightly anisotropic manner. Calculations of the electron localization function (ELF) of PbO (litharge), PbSO4 (anglesite) and PbCuSO4(OH)2 (linarite) show pronounced lone-pair character for PbO but rather isotropic ELF values around the lead cations in PbSO4 and PbCuSO4(OH)2.

The quaternary tungstates Li3Ba2RE3(WO4)8 (RE = La–Nd, Sm–Ho) were obtained by a ceramic synthesis route and were characterized by powder and single crystal X-ray diffraction. The structures of Li3Ba2Pr3(WO4)8 and Li3Ba2Tb3(WO4)8 were refined from single crystal diffractometer data: RbLiBi2(MoO4)4 type, space group C2/c, a = 528.57(2), b = 1292.39(6), c = 1934.80(10) pm, β = 91.522(4)°, 2151 F2 values, 108 parameters for Li3Ba2Pr3(WO4)8 and a = 520.54(2), b = 1272.03(6), c = 1918.85(10) pm, β = 91.948(4)°, 2020 F2 values, 108 variables for Li3Ba2Tb3(WO4)8. Striking polyhedral building units in these tungstates are WO4 tetrahedra and LiO6 octahedra, while the mixed occupied site and the barium atoms have higher coordination numbers, i.e. RE/Li@O8 and Ba@O10. In addition to the powder quality assessment by means of reflection spectroscopy, the synthesized samples were studied for their suitability as a scintillator material. Therefore, X-ray excited luminescence measurements where performed. Apart from Li3Ba2Ce3(WO4)8 and Li3Ba2Nd3(WO4)8, all compounds show strong emission under X-ray irradiation. Li3Ba2La3(WO4)8 and Li3Ba2Gd3(WO4)8 show blue CT luminescence caused by tungstate units, while the other samples show typical and multiple lines due to well known [Xe]4fn → [Xe]4fn transitions.

The scandium-rich intermetallic compounds Sc50T13In3(T = Ni, Ru, Pd) were synthesized from the elements in sealed tantalum crucibles in an induction furnace. The samples were studied through Guinier powder patterns and their structures were refined from single-crystal X-ray diffractometer data. The Sc50T13In3phases are site occupancy (coloring) variants of the aristotype Ag7+xMg26–x(Fm$$ \bar{3} $$3¯,cF264). Refinements of the occupancy parameters indicated one mixed occupied site for each crystal, leading to the refined compositions Sc50Ni13.16(1)In2.84(1), Sc49.59(1)Ru13In3.41(1), and Sc50Pd13.65(2)In2.35(2). The complex structures can be explained by a condensation of cubes (CN 8), sphenocorona (CN 10), and icosahedra (CN 12). The samples with nickel and palladium are Pauli paramagnets.Graphic abstract

Systematically twinned olivenite (Cu2(AsO4)OH) single crystals from Cap Garonne, Mine du Pradet, France, were studied by X-ray diffraction: P 21/n, a = 822.69(6) pm, b = 861.88(9) pm, c = 594.06(9) pm, β = 90.000(6)°, wR = 0.0224, 1621 F 2 values, 79 variables and a domain ratio of 0.501(1)/0.499(1). The temperature dependence of the magnetic susceptibility was well reproduced with a square-spin cluster model and an antiferromagnetic spin-exchange parameter of J/k B = 157(3) K.

The gold-rich intermetallic compounds REAu4Cd2 (RE = La–Nd, Sm) were synthesized from the elements in sealed tantalum ampoules. Their characterization by X-ray powder and single crystal data confirmed the tetragonal YbAl4Mo2 type, space group I4/mmm. The basic building units are Au4 squares (278 pm Au–Au in CeAu4Cd2) and infinite linear cadmium chains (275 pm Cd–Cd in CeAu4Cd2). We exemplarily studied the solid solution CeAu4+ x Cd2− x for x = 0–1 up to CeAu5Cd. Electron diffraction patterns on a CeAu5Cd sample confirm the single crystal data. They give no hint for complete gold-cadmium ordering. Temperature-dependent magnetic susceptibility measurements of CeAu4Cd2, CeAu5Cd, PrAu4Cd2 and NdAu4Cd2 show stable trivalent rare earth ions and give no hint for magnetic ordering above 3 K.

Natural lead dioxide samples (β modification) from Cap Garonne, Mine du Pradet, France and Mount Trevasco, Italy were studied by single crystal X-ray and electron diffraction, clearly manifesting the rutile-type structure. A needle from the Mount Trevasco sample was investigated on a single crystal diffractometer: P42/mnm, a = 495.81(10), c = 338.66(7) pm, wR = 0.0513, 117 F 2 values (all data) and nine variables (293 K data). An additional data set at T = 90 K gave no hint for structural distortions.

This work relates to the synthesis, structural, and spectroscopic characterization of praseodymium and sodium co-doped Sr3(BO3)2. This material was evaluated concerning its suitability as a photo- or radioluminescent UV-C emitting compound. Beyond recording the photoluminescence and radioluminescence, diffuse reflectance and temperature dependent spectra were recorded. Furthermore, the structure refinement based on single crystal X-ray diffraction data as well as morphologic studies by using scanning electron microscopy and dynamic light scattering methods were performed.

This work deals with the spectroscopic properties of single crystalline samples of KTb3F10. Green luminescing KTb3F10 is an efficient UV radiation converter with a quantum yield of about 40% upon UV-A excitation, while it is also an efficient scintillator upon excitation by 20–50 kV X-ray photons. The temperature dependence of the integral photoluminescence as well as the decay time of KTb3F10 monitored for the Tb3+ emission show that the internal quantum yield between 100 and 800 K is almost constant, while the external quantum yield is modulated, likely due to a change in reabsorption at elevated temperatures. In contrast, the low temperature range between 3 and 63 K reveals a change of the local Tb3+ environment in KTb3F10, which is indicated by an anomaly in the heat capacity and by a strong change of the decay time as well as by a distinct shift of the photoluminescence spectra at low temperatures. In addition, temperature dependent magnetic susceptibility measurements and a structure refinement based on single crystal X-ray diffraction data were performed.

In this chapter, the focus of Robert Karplus’s work on students’ reasoning will be revisited. The emphasis on exploring and understanding students’ reasoning in multiplicative conceptual domains, beyond the elementary school, is central in the mathematics and science education-related work of Robert Karplus. About 30 years ago, at a time when the emphasis in mathematics and science education research was on students’ achievement test scores and related statistical group averages, Robert Karplus launched a sequence of studies focusing on identifying and classifying students’ reasoning as they attempted to solve a variety of well-designed problems (or at times they were referred to as puzzles) that purposefully embedded key mathematical concepts such as proportions, control of variables, probability, correlations and others. It is the quality of students’ thinking and how they had reasoned that Karplus and his colleagues focused on, rather than the correct/incorrect answers students may have given.

The liquid CO2-extract of aged burley tobacco was investigated for its content of diterpenoids, which are considered as important precursors of flavour constituents. Among several cembranoids, already known from various tobacco types, 4,8-dimethyl-8-hydroxy-11-(1-methyl-ethyl)-14-oxo-pentadeca-5,9-diene-4-olide, a new natural product, could be identified, evidently originating from 2,6,11-cembratriene-4,8-diol by oxidative cleavage of the 11,12-double bond with subsequent cyclization to the seco-lactone 14.

The compositions of the leaf surface gums of various Nicotiana species grown under similar field conditions have been analysed and compared with those of some Nicotiana tabacum cultivars. Diterpenes could only be detected in the extracts of two of the 16 Nicotiana species; labdanoids have been detected for the first time in N. tomentosa . The relative quantitative distributions of n - and methyl-branched alkanes in the leaf surface gums proved to be specific for different species.