Homovalent Substitution Research Articles

Synergistic homovalent and heterovalent substitution effects on piezoelectric and relaxor behavior in lead-free BaTiO3 ceramics

This study investigates lead-free BaTiO3 (BT) perovskite ceramics, unraveling the synergistic effects arising from simultaneous homovalent (Zr) and heterovalent (Nb) substitution. Focusing on piezoelectric, ferroelectric, and relaxor behaviors, this research employs a comprehensive suite of analyses, including temperature-dependent dielectric measurements, polarization-electric field hysteresis loops, and bipolar strain measurements. Significantly, our study unveils that the simultaneous substitution of Zr and Nb in the BT lattice induces room-temperature relaxor behavior at relatively low concentrations (5 % Zr and 3 % Nb), yielding higher permittivity and larger maximum polarization compared to single element (Zr or Nb) substituted BT relaxors. Bipolar strain measurements showcase substantial large-signal d33* values (∼250 pm/V) across a broad temperature range (–50 °C to 30 °C) for BT ceramics with simultaneous 5 % Zr and 2 % Nb substitution. This research advances understanding of homovalent and heterovalent substitution in BT ceramics and opens avenues for tailoring properties to suit specific applications.

Systematic trends in the substitution mechanisms of minor elements in cassiterite

A dataset of 4751 EPMA point analyses on cassiterite crystals from 18 localities spanning a range of different granite-related Sn-bearing mineral systems was investigated and compared with thermodynamic considerations from speciation and lattice strain models. The existence of previously inferred charge balanced coupled substitution mechanisms of Fe3+, Fe2+, Mn2+, Nb5+, Ta5+ and W6+ for Sn4+ are confirmed. The homo­valent substitution of Sn4+ by Ti4+ and Zr4+ is also confirmed, and the first evidence for homovalent substitution of Nb4+ and W4+ in natural cassiterite is presented. The preferred substitution mechanisms for Ti, Fe, Mn, Nb, Ta, W and Zr vary systematically as a function of the mineralising environment. Cassiterite precipitated from silicate liquid dominated systems (such as in pegmatites) primarily display a coupled Fe–(Nb,Ta) substitution mechanism with a 1:2 stoichiometry, whereas cassiterite precipitated in systems dominated by autometasomatic processes (such as greisens) more closely follow a 1:1 stoichiometry, as well as increased levels of Ti. Cassiterite precipitated solely from hydrothermal fluids (such as Sn–(W) quartz vein systems) exhibit the highest Ti concentrations, with lower contents of Fe–(Nb,Ta) coupled substitutions, instead displaying a switch to the incorporation of Fe3+ via FeO.OH stoichiometry. Hydrothermally precipitated cassiterite from skarn systems display the highest Fe3+ contents, and the lowest Nb, Ta and Ti contents. These systematic changes define a continuous trend in a Ti–(Fe + Mn)–(Nb,Ta) ternary diagram, allowing for classification of the primary source of alluvial cassiterite.

AEAg7(PS4)3 (AE = Ba, Sr): The homovalent substitution of lead by alkaline earth metals achieves the separation of the two phases and enlarges the band gap

Two alkaline earth metal-containing thiophosphate compounds, BaAg7(PS4)3 and SrAg7(PS4)3, were synthesized via the homovalent substitution of Pb2+ in PbAg7(PS4)3 by Ba2+ and Sr2+, respectively. The space group of BaAg7(PS4)3 (P21/c) and SrAg7(PS4)3 (P63/m) is the same as the low- and high-temperature phases of PbAg7(PS4)3, respectively. The two compounds exhibit structural similarity and possess three-dimensional honeycomb-shaped architectures. These honeycomb structures are arranged in a layered fashion via hexagonal rings, which arise from the sharing of edges or vertices between [AgS4] and [PS4] tetrahedral, accommodating discrete entities of Ba2+ and Sr2+ cations. BaAg7(PS4)3 melts congruently with a melting point of 760 °C and a solidification point of 675 °C, while the melting behaviour of SrAg7(PS4)3 was incongruently and thermally stable up to 689 °C under vacuum of 1 × 10−3 Pa. Moreover, the band gaps of BaAg7(PS4)3 (2.69 eV) and SrAg7(PS4)3 (2.85 eV) have a significant enlargement compared to PbAg7(PS4)3 (2.09 eV). The combination of d10 cation Ag+ with second-order Jahn-Teller distortion and alkaline earth metals cation enriches the system of new metal thiophosphates and provides ideas for exploring other functional materials.

Determination of skarn garnet compositions using Raman spectroscopy

AbstractGarnet is a key and defining mineral of skarns and associated metalliferous deposits. Variation in garnet composition, commonly expressed by the proportions of different end‐members, is widely used to determine the physical–chemical features of hydrothermal fluids. Skarn garnets from the Fujiashan W‐Cu‐Mo deposit, eastern China, were investigated by Raman spectroscopy and electron probe microanalysis to assess the quantitative correlation between Raman band positions and proportions of garnet end‐members. Compositions and Raman band positions of so‐called “grandite” garnet (Adr18–98Grs0–79), where Adr and Gr are the end‐members andradite and grossular, respectively, display a spatial zonation at Fujiashan that correlates with the distance from the contact between skarn and causative intrusion. Raman band positions determined in the ranges 234–246, 351–368, 369–375, 515–544, 814–826, and 873–882 cm−1 demonstrate moderate to very strong (R2 up to 0.99) linear correlations with mol% andradite and grossular components. This is attributed to homovalent substitution between Fe3+ and Al3+ in the octahedral site, which has an indirect effect on bond lengths and angles of Si‐O vibration, resulting in linear variation of Raman band positions. The band between 515 and 544 cm−1 is the most sensitive to compositional variation, and its position enables robust estimation of end‐member proportions within 10% of results calculated from electron probe microanalysis. This research highlights the potential of Raman spectroscopy as a rapid, powerful method to assess the composition of skarn garnet, enabling accelerated construction of spatial zonation models for skarns during skarn deposit exploration.

Fine‐Tuning Single‐Source White‐Light Emission from All‐Inorganic Corrugated 2D Antimony‐Halide Perovskite (Advanced Optical Materials 17/2022)

Corrugated 2D antimony-halide perovskites such as Cs3Sb2Cl9 (CSC) are promising candidates for single-source white-light emission due to their ultra-broadband spectra. However, CSC has a serious luminescence quenching phenomenon due to inadequate confinement of excitons. In article number 2200930, Fei Xu, Xiang Wang, Feng Hong and co-workers report the homovalent substitution strategy of Sb by a small amount of rare earth cations in CSC to realize intense ultra-broadband spectra covering the visible light region at room temperature, resulting from self-trapping exciton emission, which could be considered to be attributed to high activation energy, type-I-like “straddling” band alignment, and strong electron–phonon interaction effect.

Tuning the Band Gap in the Halide Perovskite CsPbBr3 through Sr Substitution.

The ability to continuously tune the band gap of a semiconductor allows its optical properties to be precisely tailored for specific applications. We demonstrate that the band gap of the halide perovskite CsPbBr3 can be continuously widened through homovalent substitution of Sr2+ for Pb2+ using solid-state synthesis, creating a material with the formula CsPb1-xSrxBr3 (0 ≤ x ≤ 1). Sr2+ and Pb2+ form a solid solution in CsPb1-xSrxBr3. Pure CsPbBr3 has a band gap of 2.29(2) eV, which increases to 2.64(3) eV for CsPb0.25Sr0.75Br3. The increase in band gap is clearly visible in the color change of the materials and is also confirmed by a shift in the photoluminescence. Density-functional theory calculations support the hypothesis that Sr incorporation widens the band gap without introducing mid-gap defect states. These results demonstrate that homovalent B-site alloying can be a viable method to tune the band gap of simple halide perovskites for absorptive and emissive applications such as color-tunable light-emitting diodes, tandem solar cells, and photodetectors.

Fine‐Tuning Single‐Source White‐Light Emission from All‐Inorganic Corrugated 2D Antimony‐Halide Perovskite

AbstractCorrugated 2D antimony‐halide perovskites such as Cs3Sb2Cl9 (CSC) are promising candidates for single‐source white‐light emission due to their ultra‐broadband spectra. However, CSC has a serious luminescence quenching phenomenon due to inadequate confinement of excitons. By the homovalent substitution of trivalent antimony cation Sb3+ by a small amount of trivalent rare earth (RE) cations RE3+, the photoluminescence intensities from high‐quality Cs3(Sb1−xREx)2Cl9 (CSRC) (RE = Ce, Sm, Nd, Y, Er, etc.) films at room temperature (RT) are over two orders of magnitude higher than that of CSC film. Especially, the photoluminescence quantum yield (PLQY) for the Cs3(Sb0.995Er0.005)2Cl9 film is 9.5% at RT, which is much higher than A3B2X9 perovskites previously reported for single‐source white‐light lighting. Furthermore, the Cs3(Sb0.995Er0.005)2Cl9 film exhibits an ultra‐broadband emission with the full width at half maximum reaching 554 meV at RT, resulting in a “warm” white‐light with the CIE coordinate (0.33, 0.46) and the correlated color temperature of 5450 K. The PLQY enhancement can be considered as the fact that a high activation energy by bandgap widening effect and Type‐I‐like “straddling” band alignment between Cs3Sb2Cl9 and Cs3Er2Cl9 lead to reducing nonradiative losses and increasing radiative recombination channels. Meanwhile, the spectral broadening can be considered to be attributed to strong effect of electron–phonon interaction.

Structural Confinement and Energetic Matching Synergistic Effect toward a High-Energy Transfer Efficiency and a Significant Red Emission Enhancement in a Eu2+,Ln3+ Co-doped Sr9LiMn(PO4)7 Whitlockite Phosphor.

Despite an encouraging progress, Mn2+-activated red phosphors suffer from an insufficient emission intensity and a bad color purity. Thus, it is necessary to find a new strategy to realize a bright red emission through highly efficient Mn2+ sensitization. Herein, manipulating Eu2+-sensitized Sr9LiMn(PO4)7 (SLMP) composition by Ln3+ heterovalent substitution is proved to be able to substantially gain a tremendous Mn2+ emission enhancement and result in a dominant red Mn2+ emission. It is found that the emission enhancement ratio is proportional to the order of lanthanide contraction. Notably, Tb3+ doping realizes a 427-fold rise in the integrated emission intensity compared with the SLMP host, which is close to the theoretical maximum of 500. An underlying mechanism for Mn2+ red emission enhancement is proposed, which is attributed to a high-energy transfer probability from Eu2+ to Mn2+ via Ln3+-induced further structural confinement plus an energetic match effect. Meanwhile, homovalent (Ca2+) substitution could precisely tailor Mn2+ emitting color from orange-red to deep red. A warm-white LED device with a low color temperature of 3394 K, a high color-rendering index of 90.2, and suitable CIE coordinates of (0.403, 0.373) is fabricated using optimized phosphor SLMP:Eu2+, Tb3+. These results might reveal a new strategy to develop new red-emitting phosphors with a bright and highly purified red Mn2+ emission.

Crystal Structure and Theoretical Analysis of Cs2Ca3(SO4)4

Using the homovalent cation substitution strategy, a new sulfate, Cs2Ca3(SO4)4, was successfully prepared using the spontaneous crystallization technique. A single-crystal structure measurement suggested that it crystallizes in space group P21/c, with lattice parameters and molecules per unit cell of a = 9.9153(8), b = 9.3760(6), c = 9.8044(9), β = 118.365(3)°, V = 802.04(11), and Z = 2. In the structure of Cs2Ca3(SO4)4, CaO6 octahedra and SO4 tetrahedra are interconnected via a corner-sharing mode to form a three-dimensional framework comprising large cavities filled with Cs+ cations. First-principles calculations and diffuse reflectance spectra indicated that Cs2Ca3(SO4)4 has a large energy band gap. Moreover, structural comparisons with similar compounds were conducted to explain the role of cations in tuning structural symmetry and birefringence. This paper helps to explain the size effect of cations on structural evolution.

Magnesio-lucchesiite, CaMg3Al6(Si6O18)(BO3)3(OH)3O, a new species of the tourmaline supergroup

Abstract Magnesio-lucchesiite, ideally CaMg3Al6(Si6O18)(BO3)3(OH)3O, is a new mineral species of the tourmaline supergroup. The holotype material was discovered within a lamprophyre dike that cross-cuts tourmaline-rich metapelites within the exocontact of the O’Grady Batholith, Northwest Territories (Canada). Two additional samples were found at San Piero in Campo, Elba Island, Tuscany (Italy) in hydrothermal veins embedded in meta-serpentinites within the contact aureole of the Monte Capanne intrusion. The studied crystals of magnesio-lucchesiite are black in a hand sample with vitreous luster, conchoidal fracture, an estimated hardness of 7–8, and a calculated density of 3.168 (Canada) and 3.175 g/cm3 (Italy). In plane-polarized light, magnesio-lucchesiite is pleochroic (O = dark brown, E = colorless) and uniaxial (–); its refractive index values are nω = 1.668(3) and nε = 1.644(3) (Canada), and nω = 1.665(5) and nε = 1.645(5) (Italy). Magnesio-lucchesiite is trigonal, space group R3m, Z = 3, with a = 15.9910(3) Å, c = 7.2224(2) Å, V = 1599.42(7) Å3 (Canada) and with a = 15.9270(10) Å, c = 7.1270(5) Å, V = 1565.7(2) Å3 (Italy, sample 1). The crystal structure of magnesio-lucchesiite was refined to R1 = 3.06% using 2953 reflections with Fo > 4σ(Fo) (Canadian sample; 1.96% / 1225 for the Italian sample) The Canadian (holotype) sample has the ordered empirical formula X(Ca0.60Na0.39K0.01)Σ1.00Y(Mg2.02Fe0.622+Fe0.093+Ti0.25V0.01Cr0.01)Σ3.00Z(Al5.31Fe0.693+)Σ6.00[T(Si5.98Al0.02)Σ6.00O18](BO3)3V[(OH)2.59O0.41]Σ3.00W(O0.78F0.22)Σ1.00. The Italian (co-type) material shows a wider chemical variability, with two different samples from the same locality having ordered chemical formulas: X(Ca0.88Na0.12)Σ1.00Y(Mg1.45Fe0.402+Al0.79Fe0.363+)Σ3.00ZAl6[T(Si5.05Al0.95)Σ6.00O18](BO3)3V[(OH)2.90O0.10]Σ3.00W(O0.98F0.02)Σ1.00 (sample 1) and X(Ca0.71Na0.21☐0.08)Σ1.00Y(Mg2.49Fe0.412+Ti0.10)Σ3.00Z(Al5.44Fe0.463+Mg0.09V0.01)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BO3)3V(OH)3W[O0.61(OH)0.39]Σ1.00 (sample 2). Magnesio-lucchesiite is an oxy-species belonging to the calcic group of the tourmaline supergroup. It is related to lucchesiite by the homovalent substitution YFe ↔ YMg, and to feruvite by the homovalent and heterovalent substitutions YFe ↔ YMg and ZAl3+ + WO2– ↔ ZMg2+ + W(OH)1–. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2019-025). Occurrences of magnesio-lucchesiite show that its presence is not restricted to replacement of mafic minerals only; it may also form in metacarbonate rocks by fluctuations of F and Al during crystallization of common uvitic tourmaline. High miscibility with other tourmaline end-members indicates the large petrogenetic potential of magnesio-lucchesiite in Mg, Al-rich calc-silicate rocks, as well as contact-metamorphic and metasomatic rocks.

Molecular Engineering toward an Enlarged Optical Band Gap in a Bismuth Sulfate via Homovalent Cation Substitution.

Materials capable of generating coherent short-wave (<300 nm) light have attracted extensive scientific and technical interest due to their wide utilization in laser research. In this study, a the rare-earth-metal sulfate NaCe(SO4)2(H2O) (NCSO) was synthesized through a hydrothermal method, while NaBi(SO4)2(H2O) (NBSO) was successfully obtained via a homovalent cation substitution of the parent compound NCSO under hydrothermal conditions. The space groups of crystalline NCSO and NBSO are P3121 and P3221, respectively. Both compounds have similar connectivities which feature a three-dimensional channel structure formed by asymmetric [CeO9]15-/[BiO9]15- tricapped trigonal prisms and distorted [SO4]2- tetrahedra. The introduction of Bi3+ with larger ionic radii and stereochemically active lone-pair electrons simultaneously enhanced the SHG effect and band gap of NBSO in comparison to its parent compound NCSO. In contrast to NCSO, which possesses a narrow energy band gap (2.46 eV), NBSO displays the largest energy band gap (4.54 eV) among the reported bismuth sulfate NLO materials. Powder frequency-doubling-effect measurements exhibit that NCSO and NBSO possess phase-matchable SHG responses of 0.2 × KDP and 0.38 × KDP at 1064 nm, respectively. Theoretical studies have been implemented to further elucidate the structure-performance relationships of the two compounds. Experimental and theoretical studies both demonstrate that NBSO may be a promising nonlinear material applied in the short-wavelength region.

From Ce(IO3)4 to CeF2(IO3)2: fluorinated homovalent substitution simultaneously enhances SHG response and bandgap for mid-infrared nonlinear optics

An efficient mid-IR NLO material, CeF2(IO3)2, was rationally designed using a fluorinated homovalent substitution strategy.

Synthesis, structure and properties of solid solutions Ва1–хSn1+хF4 and (KyВа1–y)(1–х)Sn1+хF4–y(1–х)

We investigated the structure and electric conductivity of solid solutions of homovalent substitution Ва1–хSn1+хF4 (where х=0.03, 0.05, 0.07, 0.10, 0.15 and 0.23) and heterovalent substitution (KyВа1–y)(1–х)Sn1+хF4–y(1–х) (where х=0.03, 0.05, 0.10 and у=0.03, 0.05, 0.10) with the structure of BaSnF4. It was been found that the substitution of 7 mol.% of Ba2+ cations by Sn2+ cations contributed to an increases in electrical conductivity. The solid solution Ba0.77Sn1.23F4 had the highest electrical conductivity (573=6.8010–3 S cm–1). The substitution of barium ions by potassium ions in the BaSnF4 crystal lattice allowed reducing the conductivity of solid solutions regardless of the substituent content. Only the phases containing more than 3 mol.% of K+ ions exhibited the conductivity which exceeded the value of the initial phase at the temperatures above 385 K. In fluoride-conducting phases (KyBa1–y)(1–x)Sn1+xF4–y(1–х), the following solid solutions showed the highest electrical conductivity: (K0.05Ba0.95)0.97Sn1.03F3.95 (573=6.7810–4 S сm–1), (K0.03Ba0.97)0.95Sn1.05F3.97 (573=1.0010–3 S сm–1) and (K0.10Ba0.90)0.90Sn1.10F3.91 (573=8.7010–3 S сm–1).

Anomalously High Fluorine Mobility in Tysonite-Like LaF3:ScF3 Nanocrystals: NMR Diffusion Data

Nanosized La0.93Sc0.07F3 superionic conductor with tysonite structure was obtained at the gas–solution interface after interaction of aqueous salt solution with gaseous HF. NMR diffusion studies show that homovalent substitution of La3+ by Sc3+ with a smaller ionic radius leads to around four orders of magnitude faster fluorine diffusion as compared with crystalline LaF3 and faster as in all previously studied nanosized LaF3 and heterovalent-doped nanosized La0.95Sr0.05F2.95. The homovalent doping is a new route to improve the conductivity of tysonite-structured nanomaterials.

Incorporation of Ti into the crystal structures of the high-pressure dense silicates anhydrous phase B and superhydrous phase B

The structures of Ti-bearing anhydrous phase B and superhydrous phase B synthesized at 12 GPa/1600 °C and 21 GPa/1600 °C, respectively, have been determined by single-crystal X-ray diffraction. Anhydrous phase B has space group Pmcb. The structure of superhydrous phase B was refined in space groups Pnnm and Pnn2; crystallographic arguments unambiguously indicated that the centrosymmetric space group Pnnm is the correct choice for the crystal studied here. Ti orders at the octahedrally coordinated Si(1) site in both phases. The refined site occupancies at the Si(1) sites of anhydrous phase B and superhydrous phase B are 0.848(3) Si + 0.152 Ti and 0.92(1) + 0.08 Ti, respectively. These Ti occupancy levels correlate with a 4% expansion of the Si(1)O6 octahedron relative to values typically observed for end-member anhydrous phase B, Fe2+-bearing anhydrous phase B, and end-member superhydrous phase B. Ordering of Ti at the Si(1) is explained in terms of a homovalent substitution VISi → VITi4+, being the only option for these structures. There is no evidence for a deprotonation substitution of the kind Mg + 2OH− → Ti4+ + 2O2−, as occurs in humites. Synthesis of Ti-bearing superhydrous phase B indicates that it is stable at typical P–T conditions of the mantle transition zone and the lower mantle. Hence, water can be transported by Ti-bearing superhydrous B into the lower mantle even at temperatures of the normal mantle geotherm.

Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy): Crystal-chemical study and petrological constraints

Tourmalines from the late-Variscan Arbus pluton (SW Sardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges from schorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na + Fe2+ ↔ □ + Al, which relates schorl to foitite. The homovalent substitution (OH) ↔ F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2+ + (OH, F) ↔ Al + O relates schorl/fluor-schorl to oxy-schorl.Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite + quartz → schorl + quartz → fluor-schorl + quartz → foitite + quartz. The schorl → foitite evolution represents a distinct trend towards (Al + □) increase and unit-cell volume decrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other Li-minerals in the Arbus pluton. Tourmaline-bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle-upper crust.

A multimodal microcharacterisation of trace-element zonation and crystallographic orientation in natural cassiterite by combining cathodoluminescence, EBSD, EPMA and contribution of confocal Raman-in-SEM imaging.

In cassiterite, tin is associated with metals (titanium, niobium, tantalum, indium, tungsten, iron, manganese, mercury). Knowledge of mineral chemistry and trace-element distribution is essential for: the understanding of ore formation, the exploration phase, the feasibility of ore treatment, and disposal/treatment of tailings after the exploitation phase. However, the availability of analytical methods make these characterisations difficult. We present a multitechnical approach to chemical and structural data that includes scanning electron microscopy (SEM)-based imaging and microanalysis techniques such as: secondary and backscattered electrons, cathodoluminescence (CL), electron probe microanalyser (EPMA), electron backscattered diffraction (EBSD) and confocal Raman-imaging integrated in a SEM (RISE). The presented results show the complementarity of the used analytical techniques. SEM, CL, EBSD, EPMA provide information from the interaction of an electron beam with minerals, leading to atomistic information about their composition, whereas RISE, Raman spectroscopy and imaging completes the studies with information about molecular vibrations, which are sensitive to structural modifications of the minerals. The correlation of Raman bands with the presence/absence of Nb, Ta, Fe (heterovalent substitution) and Ti (homovalent substitution) is established at a submicrometric scale. Combination of the different techniques makes it possible to establish a direct link between chemical and crystallographic data of cassiterite.

Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks

Tourmalines, XY 3 Z 6 T 6 O 18 (BO 3 ) 3 V 3 W, are excellent petrogenetic indicators as they capture the signature of the host-rock bulk composition. Raman spectra of tourmalines can be used as fingerprints for species identification and crystal-chemical analysis. While Li-bearing species are directly distinguishable by the shape of the OH-stretching vibrations, the discrimination of Mg- and Fe-dominant species can be hindered by the coexistence of at least two types of octahedrally coordinated R n+ cations. Thirty Li-free tourmaline samples comprising 14 different species were studied by Raman spectroscopy and electron microprobe. All nine Fe 3+ -bearing samples were also analyzed by single-crystal X-ray diffraction and Mossbauer spectroscopy. The Raman scattering analysis shows that Mg-dominant species can be immediately distinguished from Fe-dominant species by the shape of the vibrational modes at ~200–240 cm −1 arising from the YO 6 vibrations. Trivalent Fe can be observed and quantified by shifts of the framework vibrations toward lower wavenumbers. The position of the main ZO 6 vibrational mode (275–375 cm −1 ) can be used to determine the Z Fe 3+ content, while the Y Fe 3+ content can be inferred from the position of the peak at ~315 cm −1 . Fits to the data points indicate that the homovalent substitution of Fe 3+ for Al 3+ leads to a considerably larger downward shift of the ZO 6 vibrational mode than the heterovalent substitution Mg 2+ for Al 3+ . The intensity ratio of the two major YO 6 vibrational modes (200–240 cm −1 ) of the fully characterized Fe 3+ -bearing samples reflects the amount of Y-site Mg and thus can be used to deduce the site-occupancy disorder of Mg over the Y and Z site for tourmaline species with Mg ≤2 apfu. By combining the information from framework and OH-stretching vibrations, Raman spectroscopy alone can be used as a micrometer-scale sensitive non-destructive method for the analysis of tourmaline crystal chemistry including trivalent Fe, which is the major tracer for oxygen fugacity and central for intersite geothermometry.

Ferrostalderite, CuFe2TlAs2S6, a new mineral from Lengenbach, Switzerland: occurrence, crystal structure, and emphasis on the role of iron in sulfosalts

AbstractThe new mineral species ferrostalderite, CuFe2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as minute, metallic, black, equant to prismatic crystals, up to 50 mu;m, associated with dolomite, realgar, baumhauerite (?) and pyrite. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 24.2/25.4; 548.3: 23.7/24.7; 586.6: 22.9/23.8; 652.3: 21.0/22.0. Electron microprobe analyses give (wt.%): Cu 6.24(25), Ag 4.18(9), Fe 9.95(83), Zn 4.46(91), Hg 1.22(26), Tl 26.86(62), As 19.05(18), Sb 0.63(6),S 25.39(47), total 97.98(72). On the basis of 12 atoms per formula unit, the chemical formula of ferrostalderite is Cu0.75(2)Ag0.30(1)Fe1.36(10)Zn0.52(11)Hg0.05(1)Tl1.00(1)[As1.94(4)Sb0.04(1)]∑1.98(4)S6.04(4). The new mineral is tetragonal, space group I4̄2 m, with a = 9.8786(5), c = 10.8489(8) Å, V = 1058.71(11) Å3, Z = 4. The main diffraction lines of the calculated powder diagram are [d (in Å), intensity, hkl]: 4.092, 70, 211; 3.493, 23, 220; 3.396, 35, 103; 3.124, 17, 310; 2.937, 100, 222; 2.656, 19, 321; 2.470, 19, 400; 2.435, 33, 303. The crystal structure of ferrostalderite has been refined by Xray single-crystal data to a final R1= 0.050, on the basis of 1169 reflections with F0 &gt; 4σ(F0). It shows a three dimensional framework of (Cu,Fe)-centred tetrahedra (1M1 + 2 M2), with channels parallel to [001] hosting disymmetric TlS6and (As,Sb)S3 polyhedra. Ferrostalderite is derived from its isotype stalderiteM1CuM2Zn2TlAs2S6through the homovalent substitution M2Zn2+ → M2Fe2+. The ideal crystal-chemical formula of ferrostalderite isM1CuM2Fe2TlAs2S6.

Charge transport in zirconium doped anatase nanowires dye-sensitized solar cells: Trade-off between lattice strain and photovoltaic parameters

Zirconium (Zr) is doped up to 5 at. % in anatase TiO2 nanowires by electrospinning and used as working electrode in dye-sensitized solar cells. Variations observed in the photovoltaic parameters were correlated by electrochemical impedance spectroscopy, open circuit voltage decay, and X-ray diffraction measurements. Results show that homovalent substitution of Zr in TiO2 increased the chemical capacitance and electron diffusion coefficient which in turn decreased charge transport resistance and charge transit time. However, lattice strain due to size mismatch between the Zr4+ and Ti4+ ions decreased open circuit voltage and fill factor thereby setting a trade-off between doping concentration and photovoltaic properties.