Polar Noncentrosymmetric ZnMoSb₂O₇ and Nonpolar Centrosymmetric CdMoSb₄O₁₀: d¹⁰ Transition Metal Size Effect Influencing the Stoichiometry and the Centricity

Two new quaternary molybdenum­(VI) antimony­(III) oxides, ZnMoSb₂O₇ and CdMoSb₄O₁₀, have been synthesized in phase-pure form. The title compounds consist of highly polarizable cations, i.e., d⁰ (Mo⁶⁺) and d¹⁰ (Zn²⁺ or Cd²⁺), and lone-pair cations (Sb³⁺). ZnMoSb₂O₇ exhibits a three-dimensional framework with ZnO₄, MoO₄, and SbO₄ polyhedra in the polar space group <i>P</i>2₁, whereas CdMoSb₄O₁₀ exhibits one-dimensional tubule structures with CdO₆, MoO₄, and SbO₃ polyhedra in the space group <i>P</i>2₁/<i>m</i>. Several synthetic efforts suggest that the the dissimilar radii of Zn²⁺ and Cd²⁺ that can accommodate polyhedra of Sb³⁺ cations influence the stoichiometry as well as the centricity for the reported materials. Spectroscopic, thermal, and elemental analyses are reported along with dipole moment calculations. Nonlinear optical properties and their structural origin are examined for polar ZnMoSb₂O₇ as well

Electric field Influence on the segregation of dopants during crystal growth by Czochralski method

Em processos de crescimento de cristais pelo método de Czochralski, é observado que um campo elétrico aplicado ao cristal durante o processo de crescimento modifica a quantidade de dopante incorporada ao cristal. É desenvolvido um modelo, baseado na teoria de Burton, Prim e Slichter, levando-se em consideração as duas classes de material envolvidas, os óxidos e os semicondutores, e os efeitos produzidos pelo campo elétrico, eletromigração, subresfriamento constitucional, Efeito Peltier e efeito Seebeck. Resultados experimentais obtidos em crescimentos de LiNbO3:Cr2O3 e Si:Al são usados para aplicações do modeloIn crystal growth processes through the Czochralski method, it is observed that an electrical field applied to the crystal during the growth process modifies the quatity of the dopant incorporated to the crystal. A model is developed based on Burton, Prim and Slichter´s theory, taking into consideration two classes of materials, the oxides and the semiconductors, and the effects produced by the electrical field, electromigration, constitutional supercooling, Peltier Effect, Seebeck Effect. Experimental results obtained from the growth of the LiNbO3:Cr2O3 e Si:Al singlecrystals are used to the model applicatio

På spaning efter elevers kunskaper, Matrisens roll i nationella historieprovets transparens

Syftet med arbetets undersökning har varit att få större förståelse för hur matriser fungerar som stödstruktur i skriftliga prov i historia. Jag har valt att undersöka om matriserna överhuvudtaget används av eleverna, om de fyller sin funktion och på vilket sätt de gör det. För att få svar på mina frågor har jag gjort en innehållsanalys av 80 elevsvar tillhörande 20 elever på fyra provuppgifter tagna ur nationella provet i historia 2013, där svar till uppgifter med matris jämförts med svar utan matris. Två av uppgifterna har mätt den källkritiska förmågan och de andra två har mätt förmågan att använda en historisk referensram. Samtidigt har en av uppgifterna inom varje kunskapsområde haft en matris som stödstruktur. Jag har kommit fram till att de elever som är vana vid att arbeta utifrån matriser verkar använda sig av dem i större utsträckning än andra i provsituationen. Utifrån det analyserade materialet har jag dragit slutsatsen att matriserna fungerar aningen bättre som stödstruktur när förmågan som bedöms inte är beroende av en specifikt historiskt referensram. Detta resultat kan också ha sin förklaring i att uppgiften kring en historisk referensram som inte hade matris har varit lättare att besvara för eleverna än det var avsett och att den jämförda uppgiften med matris har krävt mer komplexa resonemang än den utan matris. Om detta skulle bekräftas, blir min jämförelse mellan de provuppgifterna inte giltig när det gäller att dra slutsatser kring matrisens roll som stödstruktur för eleverna i besvarande av uppgiftsfrågan. Däremot tycker jag mig kunna skönja en annan funktion hos matriserna, den att de nämligen stödjer validiteten i en provuppgift

Modulation of Framework and Centricity: Cation Size Effect in New Quaternary Selenites, ASc(SeO₃)₂ (A = Na, K, Rb, and Cs)

Four new stoichiometrically equivalent quaternary scandium selenites, ASc­(SeO₃)₂ (A = Na, K, Rb, and Cs) have been hydrothermally synthesized using A₂CO₃, Sc­(NO₃)₃·<i>x</i>H₂O (or ScO₃), and SeO₂ as starting materials. All four materials share similar bond networks that are composed of corner-shared distorted ScO₆ octahedra and SeO₃ trigonal pyramids. However, each material reveals different frameworks and centricities. Detailed structural analysis suggests that the structural variation is attributed to the difference in size and subsequent coordination number for the alkali metal cations. Powder second-harmonic generation (SHG) measurements on noncentrosymmetric (NCS) RbSc­(SeO₃)₂ show that the compound has an SHG efficiency similar to that of (NH₄)­H₂PO₄. The observed SHG efficiency is due to the remaining net polarization after cancellation of oppositely aligned moments for SeO₃ and ScO₆ groups. Thorough characterizations such as spectroscopic, thermal, and elemental analyses for the new materials are presented as are dipole moment and out-of-center distortion calculations

Na_1.4InTe_3.6O_9.4: New Variant of a Hexagonal Tungsten Oxide (HTO)-Like Layered Framework Containing Both a Main-Group Cation, In³⁺, and a Lone-Pair Cation, Te⁴⁺

A novel hexagonal tungsten oxide (HTO)-like layered framework containing a main-group cation, In³⁺, and a lone-pair cation, Te⁴⁺, is reported. Na_1.4InTe_3.6O_9.4 exhibits a layered structure consisting of InO₆, TeO₃, and TeO₄ polyhedra. The synthesis, crystal structure determination, characterization, and reactivity of the material will be presented

New Polymorphs of Ternary Sodium Tellurium Oxides: Hydrothermal Synthesis, Structure Determination, and Characterization of β‑Na₂Te₄O₉ and Na₂Te₂O₆·1.5H₂O

Two new sodium tellurium oxide materials, β-Na₂Te₄O₉ and Na₂Te₂­O₆·1.5H₂O, have been synthesized through hydrothermal reactions using Na₂CO₃, TeO₂, and H₂Te­O₄·2H₂O as reagents. The structures of the novel materials have been determined by single crystal X-ray diffraction. β-Na₂Te₄O₉ is a new polymorph of ternary tellurite that is showing a three-dimensional framework structure containing only TeO₄ polyhedra. Na₂Te₂­O₆·1.5H₂O reveals an anionic layered backbone composed of Te⁶⁺O₆ octahedra and Te⁴⁺O₅ polyhedra. Thermogravimetric analyses and powder X-ray diffractions at different temperatures suggest that the frameworks of β-Na₂Te₄O₉ and Na₂Te₂­O₆·1.5H₂O are thermally stable up to 480 and 400 °C, respectively. The Na⁺ cations in between the anionic layers in Na₂Te₂­O₆·1.5H₂O are completely replaced by Li⁺ cations through an ion-exchange reaction. The UV–vis diffuse reflectance and infrared spectra, elemental analyses, and local dipole moment calculations are also reported

Structure-Directing Effect of Alkali Metal Cations in New Molybdenum Selenites, Na₂Mo₂O₅(SeO₃)₂, K₂Mo₂O₅(SeO₃)₂, and Rb₂Mo₃O₇(SeO₃)₃

Both single crystals and pure polycrystalline samples of three new quaternary alkali metal molybdenum selenites, Na₂Mo₂O₅(SeO₃)₂, K₂Mo₂O₅(SeO₃)₂, and Rb₂Mo₃O₇(SeO₃)₃, have been synthesized through hydrothermal and solid-state reactions using A₂CO₃ (A = Na, K, and Rb), MoO₃, and SeO₂ as reagents. The frameworks of all three materials consist of both families of second-order Jahn–Teller distortive cations, i.e., the d⁰ cation (Mo⁶⁺) and the lone pair cation (Se⁴⁺). Although the extent of framework distortions and the resulting occupation sites of alkali metal cations are dissimilar, Na₂Mo₂O₅(SeO₃)₂ and K₂Mo₂O₅(SeO₃)₂ exhibit similar three-dimensional networks that are composed of highly asymmetric Mo₂O₁₁ dimers and SeO₃ polyhedra. Rb₂Mo₃O₇(SeO₃)₃ reveals a two-dimensional structure that is built with Mo₃O₁₅ trimers and SeO₃ intralayer linkers. Close structural examinations suggest that the structure-directing effect of alkali metal cations is significant in determining the framework distortions and the dimensions of the molybdenum selenites. UV–vis diffuse reflectance and infrared spectroscopy, thermogravimetric analyses, and ion-exchange reactions are reported, as are out-of-center distortion and dipole moment calculations

LiSc(SeO₃)₂·<i>x</i>H₂O (0 ≤ <i>x</i> ≤ 1): New Selenites Revealing Water Molecule-Driven Extremely High Temperature Single-Crystal-to-Single-Crystal Transformations

Water molecule-driven reversible phase transitions up to 450 °C have been observed for the first time in a novel selenite crystal, LiSc­(SeO₃)₂­·H₂O, through single-crystal-to-single-crystal (SCSC) transformations. Single crystal X-ray diffraction suggests that LiSc­(SeO₃)₂­·H₂O (<i>P</i>2/<i>c</i>) transforms to LiSc­(SeO₃)₂­·0.5H₂O (<i>P</i>1̅), LiSc­(SeO₃)₂­·0.25H₂O (<i>P</i>1̅), and α-LiSc­(SeO₃)₂ (<i>I</i>–42<i>d</i>) at 170–190, 200–230, and 240–450 °C, respectively. The structural evolution is attributable to the different positions of Li⁺ cations within the eight-membered ring (8-MR) channel, in which the amount of water molecules plays a key role in determining the coordination environment and the subsequent location of Li⁺ cations. Further heating of the crystal to 500 °C results in a remarkably stable β-LiSc­(SeO₃)₂ (<i>R</i>3̅)

Na_1.4InTe_3.6O_9.4: New Variant of a Hexagonal Tungsten Oxide (HTO)-Like Layered Framework Containing Both a Main-Group Cation, In³⁺, and a Lone-Pair Cation, Te⁴⁺

A novel hexagonal tungsten oxide (HTO)-like layered framework containing a main-group cation, In³⁺, and a lone-pair cation, Te⁴⁺, is reported. Na_1.4InTe_3.6O_9.4 exhibits a layered structure consisting of InO₆, TeO₃, and TeO₄ polyhedra. The synthesis, crystal structure determination, characterization, and reactivity of the material will be presented

Designing Optical Anisotropy: Silver-Aminoalkylpyridine Nitrate Complexes with Tunable Structures

To introduce a design strategy for improving optical properties, two silver-amino alkylpyridine nitrate complexes, AgC6H8N3O3 and Ag2C14H20N6O6, were successfully synthesized using a recrystallization method. By employing polarizable π-conjugated [NO3–] ions, two types of pyridine ligands, and silver cations with a high affinity for pyridine, we obtained a one-dimensional chain structure with 4-aminomethylpyridine (AgC6H8N3O3) and a zero-dimensional molecular compound by introducing a relatively flexible aliphatic chain with 4-(2-aminoethyl)pyridine (Ag2C14H20N6O6). The compounds crystallize in the triclinic crystal system with the centrosymmetric P-1 space group, exhibiting a change in orientation between the π-conjugated system and the silver ion. Despite similar optical band gaps (3.69 eV for AgC6H8N3O3 and 3.73 eV for Ag2C14H20N6O6), AgC6H8N3O3 shows higher absorption in the 350–600 nm range. Electronic structure calculations support the ultraviolet absorption findings, suggesting that charge transfer with π-conjugated systems influences birefringence. Ag2C14H20N6O6 exhibits experimental birefringence ([email protected] nm) surpassing that of AgC6H8N3O3 ([email protected] nm), placing it among the highest recorded values within metal-pyridine incorporating nitrate complexes. The nonconventional orientation of π-conjugated [NO3–] ions contributes to this phenomenon, enhancing the action of free π-conjugated orbitals. This design strategy for micromodulating the alignment of the π-conjugated system promises to be an effective approach for enhancing optical properties, such as birefringence