Ternary phases MPtSi (M = Ca,Eu, Sr,Ba) with the LalrSi-type structure

Four ternary phases MPtSi (M = Ca, Eu, Sr, Ba) have been shown to crystallize in the LaIrSi-type structure (space group P2₁3). This ternary structure is a derivative structure of the binary SrSi₂-type structure (space group P4₃32 or P4₁32). In the MPtSi series the LaIrSi-type structure has a stability range for metals with radii from r_Ca = 1.973 Å to r_Ba = 2.243 Å in contrast to MSi₂ compounds which exist with the SrSi₂-type structure only from r_Sr = 2.151Å to r_Ba 2.243 Å. From a single-crystal investigation on CaPtSi remarkably short PtSi distances of 2.30 Å (3x) are obtained. Structural relations are discussed.     

Optical Temperature-Sensing Performance of Nd3+:MF2 (M=Ba,Ca, Sr) Crystalline Powders Prepared by Combustion Synthesis

There is a large interest in luminescent materials for application as temperature sensors. In this scenario, we investigate the performance of neodymium-doped alkaline-earth fluoride (Nd³⁺:MF₂; M=Ba, Ca, Sr) crystalline powders prepared by combustion synthesis for optical temperature-sensing applications based on the luminescence intensity ratio (LIR) technique. We observe that the near-infrared luminescence spectral profile of Nd³⁺ changes with the temperature in a way that its behavior is suitable for optical thermometry operation within the first biological window. We also observe that the thermometric sensitivities of all studied samples change depending on the spectral integration range used in the LIR analysis. Nd³⁺:CaF₂ presents the largest sensitivity values, with a maximum absolute sensitivity of 6.5×10⁻³/K at 824 K and a relative sensitivity of 1.71 %/K at human-body temperature (310 K). The performance of CaF₂ for optical thermometry is superior to that of β-NaYF₄, a standard material commonly used for optical bioimaging and temperature sensing, and on par with the most efficient oxide nanostructured materials. The use of thermometry data to help understand structural properties via Judd-Ofelt intensity standard parameters is also discussed.     

Eu2+在碱土金属氟卤化物MFX(M=Ca、Sr或Ba,X=Cl、Br或I)中的发光

我们合成了六种Eu²⁺激活的碱土金属氟卤化物MFX:Eu²⁺(M=Ca、Sr或Ba;X=Cl、Br或I)。研究了它们的荧光发射光谱和激发光谱,讨论了Eu²⁺离子的跃迁发射随基质晶体组成和结构变化的规律。根据晶体场理论,按照C_4v点对称性,计算得到在MFCl:Eu²⁺(M=Ca、Sr或Ba)晶体中Eu²⁺离子的4?⁶5d¹激发态能级分裂的数值。     

Two novel acentric borate fluorides: M3B6O11F2 (M = Sr, Ba)

Two novel, noncentrosymmetric borate fluorides, Sr(3)B(6)O(11)F(2) and Ba(3)B(6)O(11)F(2), have been synthesized hydrothermally and their structures determined. The compounds are isostructural, crystallizing in space group P2(1), having lattice parameters of a = 6.4093 (13) ?, b = 8.2898 (17) ?, c = 9.3656 (19) ?, and β = 101.51 (3)° for Sr(3)B(6)O(11)F(2) and a = 6.5572 (13) ?, b = 8.5107 (17) ?, c = 9.6726 (19) ?, and β = 101.21 (3)° for Ba(3)B(6)O(11)F(2). The structure consists of a complex triple-ring borate framework having aligned triangular [BO(3)] groups that impart polarity. Fluorine atoms are bound only to the alkaline-earth metals and are not part of the borate framework, resulting in a vastly different structure from those of the hydrated borates Sr(3)B(6)O(11)(OH)(2) and Ba(3)B(6)O(11)(OH)(2) with similar formulas. The title compounds are transparent to nearly 200 nm, making them potentially useful for deep-ultraviolet nonlinear-optical applications.     

Effect of pressure on the structures of divalent metal disilicides MSi2 (M = Ca,Eu, Sr)

After high-pressure/high-temperature treatment (40 kbar at 1000–1500°C) and quenching to ambient conditions CaSi₂, EuSi₂, and SrSi₂ crystallize in the α-ThSi₂ type of structure. Lattice constants and positional parameters have been determined by X-ray powder technique. Structural relations are discussed.     

碱土金属铝酸盐系列长余辉磷光体的制备研究

研究了MAl2O4∶Eu2+(M=Ca,Sr,Ba)磷光体的制备过程,通过向磷光体中引入微量Dy3+,B3+等添加剂离子,得到了发绿色光的超长余辉磷光体,余辉发光初始亮度达4.8cd·m-2,激发停止50h后,其余辉发光仍清晰可见。制备出发紫色光、蓝色光及黄色光的碱土金属铝酸盐系列长余辉磷光体。分析了各磷光体发射光谱、激发光谱及余辉发光,讨论了磷光体的光谱移动以及Eu2+在碱土金属铝酸盐中的发光。     

Extreme High-Voltage Electroconductivity of Molten KCl–MCl2 (M = Ca,Sr, Ba)

The electroconductivity of molten mixtures of calcium, strontium, and barium chlorides with potassium chloride (component concentrations 0, 25, 50, 75, 100 mol %) is studied as a function of the electric field strength. Isotherms of extreme high-voltage conductivities of the mixtures are an additive function of the composition, as opposed to isotherms of low-voltage conductivity, which exhibit considerable deviations and pass through minimums.     

Nitridophosphate-Based Ultra-Narrow-Band Blue-Emitters: Luminescence Properties of AEP8N14:Eu2+ (AE=Ca,Sr, Ba)

The nitridophosphates AEP₈N₁₄ (AE=Ca, Sr, Ba) were synthesized at 4–5 GPa and 1050–1150 °C applying a 1000 t press with multianvil apparatus, following the azide route. The crystal structures of CaP₈N₁₄ and SrP₈N₁₄ are isotypic. The space group Cmcm was confirmed by powder X-ray diffraction. The structure of BaP₈N₁₄ (space group Amm2) was elucidated by a combination of transmission electron microscopy and diffraction of microfocused synchrotron radiation. Phase purity was confirmed by Rietveld refinement. IR spectra are consistent with the structure models and the chemical compositions were confirmed by X-ray spectroscopy. Luminescence properties of Eu²⁺-doped samples were investigated upon excitation with UV to blue light. CaP₈N₁₄ (λ_em=470 nm; fwhm=1380 cm⁻¹) and SrP₈N₁₄ (λ_em=440 nm; fwhm=1350 cm⁻¹) can be classified as the first ultra-narrow-band blue-emitting Eu²⁺-doped nitridophosphates. BaP₈N₁₄ shows a notably broader blue emission (λ_em=417/457 nm; fwhm=2075/3550 cm⁻¹).     

MO-RE2O3-B2O3(M=Mg,Ca,Sr,Ba;RE=La,Eu,Gd)玻璃的发光性质

在空气中采用高温固相反应方法合成的17MO－（8-x-y)-75B2O3-xGd2O3(MLBEG,M-Mg,Ca,Sr,Ba)玻璃，在紫外光（λex=350nm)激发下发射蓝光和红光，在绿色光（λex=532nm)激发下发射红光，电子自旋共振谱研究表明玻璃体系中有Eu^2 离子存在，蓝色区的宽带发射是Eu^2 离子的5d-4f跃迁发射：红色区的窄带发射是Eu^3 离子的5Do-7FJ(J=1,2,3,4)跃迁发射，发现玻璃中的碱土金属离子对Eu^3 /Eu^2 离子的比例有很大影响，选择不同的碱土金属离子可以调节玻璃蓝色光和红色光的相对发射强度，MLBEG玻璃的发光性质可用于转换太阳能，增强植物的光合作用。     

The Periodate‐Based Double Perovskites M2NaIO6 (M = Ca,Sr, and Ba)

The crystal structures of the M₂NaIO₆ series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X‐ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I^– with O₂^(air) to I⁷⁺ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali‐metal periodate with the alkaline‐earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Å, whereas the strontium and calcium compounds crystallize in the monoclinic space group P2₁/c (no. 14) with a = 5.7600(1) Å, b = 5.7759(1) Å, c = 9.9742(1) Å, β = 125.362(1)° and a = 5.5376(1) Å, b = 5.7911(1) Å, c = 9.6055(1) Å, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba₂NaIO₆ contains the first perfectly octahedral [IO₆]^5– unit reported. The compounds of the ortho‐periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR‐ and Raman‐active vibrations.     

Eu2+/Mn2+激活的M3MgSi2O8-M2SiO4(M=Ba,Ca)荧光粉的发光特性

采用高温固相法制备了Eu2+/Mn2+单激活和共激活的M3MgSi2O8-M2SiO4(M=Ba,Ca)两相荧光粉.通过X射线衍射(XRD)和荧光光谱(PL)对样品材料的晶体结构和光谱性能进行了表征.XRD测试结果表明所合成的样品具有M3MgSi2O8和M2SiO4两种晶相结构.PL测试显示,Eu2+在Ba3MgSi2O8-Ba2SiO4体系中发射442和502nm两个波带的光;而Eu2+在Ca2+部分取代Ba2+的BaCa2MgSi2O8-Ba1.31Ca0.69SiO4体系中发射420～520nm的连续波带,并且激发光谱向长波扩展,更加适用于被InGaN芯片(395 nm)激发.通过改变Mn2+的掺杂量可制得颜色可调的BaCa2MgSi2O8-Ba1.31Ca0.69SiO4:Eu2+,Mn2+白光荧光粉.     

碱土金属钛酸盐-TiO2异质结型复合光催化活性研究

采用溶胶-凝胶法制备碱土金属钛酸盐MTiO3(M=Mg,Ca,Sr,Ba),并进一步与TiO2固相法复合制备MTiO3-TiO2异质结型复合光催化剂.以光催化降解亚甲基蓝(MB)为探针,评价了MTiO3和MTiO3-TiO2光催化剂的活性变化.结果表明,紫外光条件下碱土金属钛酸盐MTiO3的光催化活性顺序为:CaTiO3>BaTiO3>SrTiO3>MgTiO3,钙钛矿化合物的容忍因子、电负性以及催化剂的吸附性能都影响催化剂的降解效率.MTiO3与TiO2复合后形成的异质结复合光催化剂的催化活性得到显著的提高,催化剂浓度1.0g/L时,光催化反应1h后,MB(25mg/L)的降解率分别为82.6%,99.8%,93.7%,97.3%,异质结复合光催化剂活性顺序与MTiO3一致.光催化活性的提高与异质结界面形成电荷定向流动,促进光生电子、空穴的分离有关.     

Bare and ligand protected planar hexacoordinate silicon in SiSb3M3+ (M = Ca,Sr, Ba) clusters

The occurrence of planar hexacoordination is very rare in main group elements. We report here a class of clusters containing a planar hexacoordinate silicon (phSi) atom with the formula SiSb₃M₃⁺ (M = Ca, Sr, Ba), which have D_3h (¹A₁′) symmetry in their global minimum structure. The unique ability of heavier alkaline-earth atoms to use their vacant d atomic orbitals in bonding effectively stabilizes the peripheral ring and is responsible for covalent interaction with the Si center. Although the interaction between Si and Sb is significantly stronger than the Si–M one, sizable stabilization energies (−27.4 to −35.4 kcal mol⁻¹) also originated from the combined electrostatic and covalent attraction between Si and M centers. The lighter homologues, SiE₃M₃⁺ (E = N, P, As; M = Ca, Sr, Ba) clusters, also possess similar D_3h symmetric structures as the global minima. However, the repulsive electrostatic interaction between Si and M dominates over covalent attraction making the Si–M contacts repulsive in nature. Most interestingly, the planarity of the phSi core and the attractive nature of all the six contacts of phSi are maintained in N-heterocyclic carbene (NHC) and benzene (Bz) bound SiSb₃M₃(NHC)₆⁺ and SiSb₃M₃(Bz)₆⁺ (M = Ca, Sr, Ba) complexes. Therefore, bare and ligand-protected SiSb₃M₃⁺ clusters are suitable candidates for gas-phase detection and large-scale synthesis, respectively.

The global minimum of SiSb₃M₃⁺ (M = Ca, Sr, Ba) is a D_3h symmetric structure containing an elusive planar hexacoordinate silicon (phSi) atom. Most importantly, the phSi core remains intact in ligand protected environment as well.

Exploring the bonding capacity of main-group elements (such as carbon or silicon) beyond the traditional tetrahedral concept has been a fascinating subject in chemistry for five decades. The 1970 pioneering work of Hoffmann and coworkers¹ initiated the field of planar tetracoordinate carbons (ptCs), or more generally, planar hypercoordinate carbons. The past 50 years have witnessed the design and characterization of an array of ptC and planar pentacoordinate carbon (ppC) species.^2–14 However, it turned out to be rather challenging to go beyond ptC and ppC systems. The celebrated CB₆²⁻ cluster and relevant species^15,16 were merely model systems because C avoids planar hypercoordination in such systems.^17,18 In 2012, the first genuine global minimum D_3h CO₃Li₃⁺ cluster was reported to have six interactions with carbon in planar form, although electrostatic repulsion between positively charged phC and Li centers and the absence of any significant orbital interaction between them make this hexacoordinate assignment questionable.¹⁹ It was only very recently that a series of planar hexacoordinate carbon (phC) species, CE₃M₃⁺ (E = S–Te; M = Li–Cs), were designed computationally by the groups of Tiznado and Merino (Fig. 1; left panel),²⁰ in which there exist pure electrostatic interactions between the negative C^δ− center and positive M^δ+ ligands. These phC clusters were achieved following the so-called “proper polarization of ligand” strategy.Open in a separate windowFig. 1The pictorial depiction of previously reported phC CE₃M₃⁺ (E = S–Te; M = Li–Cs) clusters and the present SiE₃M₃⁺ (E = S–Te and N–Sb; M = Li–Cs and Ca–Ba) clusters. Herein the solid and dashed lines represent covalent and ionic bonding, respectively. The opposite double arrows illustrate electrostatic repulsion.The concept of planar hypercoordinate carbons has been naturally extended to their next heavier congener, silicon-based systems. Although the steric repulsion between ligands decreases due to the larger size, the strength of π- and σ-bonding between the central atom and peripheral ligands dramatically decreases, which is crucial for stability. Planar tetracoordinate silicon (ptSi) was first experimentally observed in a pentaatomic C_2v SiAl₄⁻ cluster by Wang and coworkers in 2000.²¹ Very recently, this topic got a huge boost by the room-temperature, large-scale syntheses of complexes containing a ptSi unit.²² A recent computational study also predicted the global minimum of SiMg₄Y⁻ (Y = In, Tl) and SiMg₃In₂ to have unprecendented planar pentacoordinate Si (ppSi) units.²³ Planar hexacoordinate Si (phSi) systems seem to be even more difficult to stabilize. Previously, a C_2v symmetric Cu₆H₆Si cluster was predicted as the true minimum,²⁴ albeit its potential energy surface was not fully explored. A kinetically viable phSi SiAl₃Mg₃H₂⁺ cluster cation was also predicted.²⁵ However, these phSi systems^24,25 are only local minima and not likely to be observed experimentally. In 2018, the group of Chen identified the Ca₄Si₂²⁻ building block containing a ppSi center and constructed an infinite CaSi monolayer, which is essentially a two-dimensional lattice of the Ca₄Si₂ motif.²⁶ Thus, it is still an open question to achieve a phSi atom to date.Herein we have tried to find the correct combination towards a phSi system as the most stable isomer. Gratifyingly, we found a series of clusters, SiE₃M₃⁺ (E = N, P, As, Sb; M = Ca, Sr, Ba), having planar D_3h symmetry with Si at the center of the six membered ring, as true global minimum forms. Si–E bonds are very strong in all the clusters, and alkaline-earth metals interact with the Si center by employing their d orbitals. However, electrostatic repulsion originated from the positively charged Si and M centers for E = N, P, and As dominates over attractive covalent interaction, making individual Si–M contacts repulsive in nature. This makes the assignment of SiE₃M₃⁺ (E = N, P, As; M = Ca, Sr, Ba) as genuine phSi somewhat skeptical. SiSb₃M₃⁺ (M = Ca, Sr, Ba) clusters are the sole candidates which possess genuine phSi centers as both electrostatic and covalent interactions in Si–M bonds are attractive. The d orbitals of M ligands play a crucial role in stabilizing the ligand framework and forming covalent bonds with phSi. Such planar hypercoordinate atoms are, in general, susceptible to external perturbations. However, the present title clusters maintain the planarity and the attractive nature of the bonds even after multiple ligand binding at M centers in SiSb₃M₃(NHC)₆⁺ and SiSb₃M₃(Bz)₆⁺. This would open the door for large-scale synthesis of phSi as well.Two major computational efforts were made before reaching our title phSi clusters. The first one is to examine SiE₃M₃⁺ (E = S–Po; M = Li–Cs) clusters, which adopt D_3h or C_3v structures as true minima (see Table S1 in ESI^†), being isoelectronic to the previous phC CE₃M₃⁺ (E = S–Po; M = Li–Cs) clusters. In the SiE₃M₃⁺ (E = S–Po; M = Li–Cs) clusters, the Si center always carries a positive charge ranging from 0.01 to +1.03|e|, in contrast to the corresponding phC species (see Fig. 1). Thus, electrostatic interactions between the Si^δ+ and M^δ+ centers would be repulsive (Fig. 1). Given that the possibility of covalent interaction with an alkali metal is minimal, it would be a matter of debate whether they could be called true coordination. A second effort is to tune the electronegativity difference between Si and M centers so that the covalent contribution in Si–M bonding becomes substantial. Along this line, we consider the combinations of SiE₃M₃⁺ (E = N, P, As, Sb; M = Be, Mg, Ca, Sr, Ba). The results in Fig. S1^† show that for E = Be and Mg, the phSi geometry has a large out-of-plane imaginary frequency mode, which indicates a size mismatch between the Si center and peripheral E₃M₃ (E = N–Bi; M = Be, Mg) ring. On the other hand, the use of larger M = Ca, Sr, Ba atoms effectively expands the size of the cavity and eventually leads to perfect planar geometry with Si atoms at the center as minima. In the case of SiBi₃M₃⁺, the planar isomer possesses a small imaginary frequency for M = Ca. Although planar SiBi₃Sr₃⁺ and SiBi₃Ba₃⁺ are true minima, they are 2.2 and 2.5 kcal mol⁻¹ higher in energy than the lowest energy isomer, respectively (Fig. S2^†). Fig. 2 displays some selected low-lying isomers of SiE₃M₃⁺ (E = N, P, As, Sb; M = Ca, Sr, Ba) clusters (see Fig. S3–S6^† for additional isomers). The global minimum structure is a D_3h symmetric phSi with an ¹A₁′ electronic state for all the twelve cases. The second lowest energy isomer, a ppSi, is located more than 49 kcal mol⁻¹ above phSi for E = N. This relative energy between the most stable and nearest energy isomer gradually decreases upon moving from N to Sb. In the case of SiSb₃M₃⁺ clusters, the second-lowest energy isomer is 4.6–6.1 kcal mol⁻¹ higher in energy than phSi. The nearest triplet state isomer is very high in energy (by 36–53 kcal mol⁻¹, Fig. S3–S6^†) with respect to the global minimum.Open in a separate windowFig. 2The structures of low-lying isomers of SiE₃M₃⁺ (E = N, P, As, Sb; M = Ca, Sr, Ba) clusters. Relative energies (in kcal mol⁻¹) are shown at the single-point CCSD(T)/def2-TZVP//PBE0/def2-TZVP level, followed by a zero-energy correction at PBE0. The values from left to right refer to Ca, Sr, and Ba in sequence. The group symmetries and electronic states are also given.Born–Oppenheimer molecular dynamics (BOMD) simulations at room temperature (298 K), taking SiE₃Ca₃⁺ clusters as case studies, were also performed. The results are displayed in Fig. S7.^† All trajectories show no isomerization or other structural alterations during the simulation time, as indicated by the small root mean square deviation (RMSD) values. The BOMD data suggest that the global minimum also has reasonable kinetic stability against isomerization and decomposition.The bond distances, natural atomic charges, and bond indices for SiE₃Ca₃⁺ clusters are given in † for M = Sr, Ba). The Si–E bond distances are shorter than the typical Si–E single bond distance computed using the self-consistent covalent radii proposed by Pyykkö.²⁷ In contrast, the Si–M bond distance is almost equal to the single bond distance. This gives the first hint of the presence of covalent bonding therein. However, the Wiberg bond indices (WBIs) for the Si–M links are surprisingly low (0.02–0.04). We then checked the Mayer bond order (MBO), which can be seen as a generalization of WBIs and is more acceptable since the approach of WBI calculations assumes orthonormal conditions of basis functions while the MBO considers an overlap matrix. The MBO values for the Si–M links are now sizable (0.13–0.18). These values are reasonable considering the large difference in electronegativity between Si and M, and, therefore, only a very polar bond is expected between them. In fact, the calculations of WBIs after orthogonalization of basis functions by the Löwdin method gives significantly large bond orders (0.48–0.55), which is known to overestimate the bond orders somewhat. The above results indicate that the presence of covalent bonding cannot be ruled out only by looking at WBI values.Bond distances (r, in Å), different bond orders (WBIs) {MBOs} [WBI in orthogonalized basis], and natural atomic charges (q, in |e|) of SiE₃Ca₃⁺ (E = N, P, As, Sb) clusters at the PBE0/def2-TZVP level

掺杂铕和铽的卤硼酸盐荧光体的制备及光谱特征

采用高温固相法在空气中合成了一系列掺杂稀土离子的卤硼酸盐荧光体, 研究了其发光性质和基质组成对稀土离子共掺杂的荧光体发光性质的影响. 研究结果表明, 在Eu3+和Tb3+共掺杂的体系中存在电子转移, 因此出现了Eu3+, Eu2+和 Tb3+共存于同一基质共同发射的现象. Ce3+对Eu2+和Tb3+具有敏化作用, 可增强其发射强度. 基质的组成对稀土离子的发射峰位和发射强度有明显影响.     

Contribution a l'etude des systemes Ca3(PO4)2-MSO4 (M=Sr,Ba)

In the systems Ca₃(PO₄)₂-MSO₄ (M = Sr, Ba), the series of single phase Ca_21?3xM_2xI(PO₄)_14?2x(SO₄)_2x with 0<x<0.15 forM=Sr and 0<x<0.1 forM = Ba have been prepared. These solid solutions, respectively strontium phosphosulfate and barium phosphosulfate, are isostructural with anhydrous tricalcium orthophosphate. They have been characterized by their infrared spectra and their crystallographic unit cell parameters.     

Alkaline Earth Metal Zirconate Perovskites MZrO3 (M=Ba2+, Sr2+, Ca2+) Derived from Molecular Precursors and Doped with Eu3+ Ions

The effect of alkaline earth metal alkoxides on the protonation of zirconocene dichloride was investigated. This approach enabled the design of compounds with preset molecular structures for generating high‐purity binary metal oxide perovskites MZrO₃ (M=Ba²⁺, Sr²⁺, Ca²⁺). Single‐source molecular precursors [Ba₄Zr₂(μ₆‐O)(μ₃,η²‐OR)₈(OR)₂(η²‐HOR)₂(HOR)₂Cl₄], [Sr₄Zr₂(μ₆‐O)(μ₃,η²‐OR)₈(OR)₂(HOR)₄Cl₄], [Ca₄Zr₂(μ₆‐O)(μ₃,η²‐OR)₈(OR)₂Cl₄], and [Ca₆Zr₂(μ₂,η²‐OR)₁₂(μ‐Cl)₂(η²‐HOR)₄Cl₆] ? 8 CH₂Cl₂ were prepared via elimination of the cyclopentadienyl ring from Cp₂ZrCl₂ as CpH in the presence of M(OR)₂ and alcohol ROH (ROH=CH₃OCH₂CH₂OH) as a source of protons. The resulting complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single‐crystal X‐ray diffraction. The compounds were then thermally decomposed to MCl₂/MZrO₃ mixtures. Leaching of MCl₂ from the raw powder with deionized water produced highly pure perovskite‐like oxide particles of 40–80 nm in size. Luminescence studies on Eu³⁺‐doped MZrO₃ revealed that the perovskites are attractive host lattices for potential applications in display technology.     

Synthesis of alkaline earth diazenides M(AE)N2 (M(AE) = Ca, Sr, Ba) by controlled thermal decomposition of azides under high pressure

The alkaline earth diazenides M(AE)N(2) with M(AE) = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at high-pressure/high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) ?, c = 5.9844(9) ?, Z = 2, wR(p) = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN(2) and BaN(2). Accordingly, CaN(2) is isotypic with SrN(2) (space group I4/mmm (no. 139), a = 3.8054(2) ?, c = 6.8961(4) ?, Z = 2, wR(p) = 0.057) and the corresponding alkaline earth acetylenides (M(AE)C(2)) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN(2) adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) ?, b = 4.3776(3) ?, c = 7.2188(4) ?, β = 104.9679(33)°, Z = 4 and wR(p) = 0.049). The N-N bond lengths of 1.202(4) ? in CaN(2) (SrN(2) 1.239(4) ?, BaN(2) 1.23(2) ?) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N(2)](2-). Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides M(AE(2))N (M(AE) = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm(-1) assigned to the N-N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.     

Structure Prediction of Binary Pernitride MN2 Compounds (M=Ca,Sr, Ba,La, and Ti)

Metal‐pernitride compounds belong to a class of chemical systems in which both the complex ions and the non‐bonding electrons may play roles in the formation of their modified crystalline structures. To investigate this issue, the energy landscapes of pernitrides of metals with different maximum valence (M=Ca, Sr, Ba, La, and Ti) were globally explored on the ab initio level at standard and high pressures, thereby yielding possible (meta)stable modifications in these systems together with information on how the landscape changed as function of the valence of the metal cation. For all of the systems in which no compounds had been synthesized so far, we predicted the existence of kinetically stable modifications that should, in principle, be experimentally accessible. In particular, TiN₂ should crystallize in a new structure type, TiN₂‐I.     

Conductivity of nonstoichiometric fluorides LnF2+x (Ln = Sm,Eu, Yb)

Nonstoichiometric fluorides LnF_2+x (Ln = Sm, Eu, Yb) were synthesized by reduction of trifluorides with the above rare-earth elements. The resulting phases were identified by chemical and X-ray phase analyses, their composition and structure were determined, and their lattice constants were found. The ac bridge method at a frequency of 70 kHz was used to study the conductivity of the synthesized compounds and starting trifluorides in the temperature range 773–298 K. The temperature dependence of the conductivity of these compounds is satisfactorily approximated by the Arrhenius-Frenkel equation. A kink is observed on the plots of the electrical conductivity against temperature for all compounds. With decreasing content of fluorine, this kink shifts to higher temperatures. The highest conductivity is observed for the phases with low crystal packing density. With increasing content of fluorine, the conductivity of all nonstoichiometric phases not belonging to substitution solid solutions approaches the conductivity of the corresponding trifluorides.     

Thermoanalytical study of the formation of compounds in the PbO−MO (M=Ca,Sr, Ca+Sr) system

In order to clarify the effect of PbO addition on the formation steps of the superconducting phases in the system Bi₂O₃?SrO?CaO?CuO, a study of solid-state reactions under non-isothermal conditions, in the PbO?MO (M=Ca, Sr, Ca+Sr) system has been carried out. Results suggest that the reactivity of the components in the system containing PbO and CaO is much higher than in the system containing SrO. The Ca₂PbO₄ compound is formed first even in the system whereM=Ca+Sr. It is confirmed that Ca₂PbO₄ systems containing PbO.