Search

A structural features, real compositions, and point defects of nominally pure and Cr- and Ni-doped Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN) crystals, which structure contains four chemically-different and ten crystallochemically-different atoms, have been determined using neutron, X-ray single crystal, X-ray powder, and X-ray synchrotron diffraction techniques, and EXAFS/XANES spectroscopy. The location of transition metal ions has been identified based on the analysis of electron (nuclear) density and confirmed by the EXAFS/XANES together with the definition of formal charges of Ni atoms in Ni-doped SBN crystals. The scope and application possibilities of diffraction methods and EXAFS/XANES spectroscopy for the determination of structural features and defect formation in functional bulk nominally-pure and Cr- and Ni-doped Sr 0.61 Ba 0.39 Nb 2 O 6 single crystals is established. [ABSTRACT FROM AUTHOR]

Whitlockite-type polycrystalline and single-crystal (Ca 3− x Sr x)(VO 4) 2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca 3− x Sr x)(VO 4) 2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca 1.8 Sr 1.2)(VO 4) 2 (CSVO) revealed its actual composition (Ca 2.982(11) Sr 0.031)(VО 4) 2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5 A sites, forming two independent strongly distorted tetrahedral Ca5O 4 and octahedral Ca5 A O 6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa 2.4 Sr 0.6)(VO 4) 2 doped with 0.5 and 1.0 wt% Tm 2 O 3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5 A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca 2.776(7) Sr 0.210(4) Tm3+ 0.008(1))(VO 4) 2 and (Ca 2.855(7) Sr 0.140(7) Tm3+ 0.009(1) □ 0.022(7))(VO 4) 2 , respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed. • Polycrystalline and single-crystal (Ca 3− x Sr x)(VO 4) 2 with х = 0.3–1.35 are grown. • Sr2+ partially occupies monocapped Ca2 and two-capped Ca3 trigonal prismatic sites. • In Tm-doped (Ca 3− x Sr x)(VO 4) 2 , Sr2+ and Tm3+ are located in octahedral Ca4 site. • A formal charge 3+ and 8-coordinated oxygen environment is established for Tm. • Additional interstitial oxygen and vacancies in the Ca1 site are found. [ABSTRACT FROM AUTHOR]

Nanocomposites based on nickel sulfate hexahydrate α-NiSO 4 ·6H 2 O (NSH) with titanium (IV) oxide introduced in the form of nanoparticles (Hombifine N: anatase; Degussa P25: 85 % anatase + 15 % rutile; η-phase: 86 % η - phase + 14 % anatase, NSH:Ti(1)) or sols (NSH:Ti(2)) are synthesized for the first time. X-ray diffraction study reveals a single-phase nature of samples, the full occupancy of all crystallographic sites in the NSH:Ti(1) structures, and the presence of Ti4+ ions in interstitial sites near the vacant Ni site in the NSH:Ti(2) structures. A crystallization of the nanosized η-phase of the composition TiO 2- x × m H 2 O directly in the NSH:Ti(1) crystalline matrix with the formation of TiO 2 with the rutile structure, facilitated by the structural-geometric correspondence of 2D projections of NSH and rutile, is observed for the first time. The presence of TiO 2 in the interblock space of NSH:Ti(1) crystals affects the unit cell parameters due to the induced stresses, which is practically not described in the literature. The intensity of SHG signals of NSH:Ti varies depending on both the prehistory of TiO 2 samples and the crystal state, single-crystal or powdered, of the object under study: the highest values were observed for the NSH:Ti(2) powder with the lowest content of titanium ions. The UV–VIS study reveals similar absorption and transmission bands, but with little difference in band width and intensity, for NSH, NSH:Ti(1) and NSH:Ti(2), which can be perspective for UV filters operating in the solar-blind range. • Nanocomposites based on NiSO 4 ·6H 2 O with TiO 2 nanoparticles or sols are synthesized. • The presence of Ti4+ ions in interstitial sites near the vacant Ni site is found. • Rutile structure with Ti4+ octahedra is formed in the interblock space of NSH. • Intensity of SHG signals varies depending on prehistory of TiO 2 samples. • NSH:Ti possesses promising spectroscopic properties for solar-blind UV filters. [ABSTRACT FROM AUTHOR]

Promising luminescent CsCd X 3 (X = Cl, Br) single crystals, both nominally-pure and doped with bismuth, have been studied comprehensively by X-ray diffraction, X-ray synchrotron radiation, and X-ray absorption spectroscopy. Crystal structure refinement shows vacancies in the Cs crystallographic site and partial substitution of Cd2+ ions by Bi3+ ones in both CsCdCl 3 and CsCdBr 3 (point defects Bi Cd •), which is consistent with the results of X-ray absorption spectroscopy. The assumed presence of Bi1+ ions in the Cs1+ sites of doped CsCd X 3 (X = Cl, Br) crystals is not confirmed. In the photoluminescence spectra of Bi-doped CsCdCl 3 and CsCdBr 3 crystals, a single band in the near-IR spectral range with a maximum around 1000 nm is caused by point defects Bi Cd •. Photoluminescence spectra and decay kinetics of Bi-doped CsCd X 3 (X = Cl, Br) indicate their promising use as luminescent materials. • Bi-doped CsCd X 3 (X = Cl, Br) crystals were grown by the Bridgman-Stockbarger method. • Crystal structures were refined using X-ray diffraction and synchrotron radiation. • Vacancies in the Cs site and a partial substitution of Cd2+ by Bi3+ were found. • The photoluminescence band around 1000 nm is caused by Bi Cd.• point defects. • Photoluminescence studies and decay kinetics indicate the luminescent properties. [ABSTRACT FROM AUTHOR]

Doping-induced structural changes of Co-activated calcium orthovanadate Ca 3 (VO 4) 2 (CVO) single crystals and specific local behavior of cobalt ions depending on the dopant content are presented in this paper. CVO is activated with over-stoichiometric Co 3 O 4 of different concentration (CVO: x Co; x ​= ​0.1, 0.5, 1.0, 1.5, 2.0 ​wt %) during the Czochralski growth. Single-crystal synchrotron X-ray diffraction study shows gradual increase in the number of Ca crystallographic sites occupied by cobalt ions with increasing dopant concentration: from Ca3 site for CVO:0.1Co to additionally Ca2 and Ca4 sites for CVO:0.5–1.5Co, and also to Ca1 site for CVO:2.0Co. Vacancies in the tetrahedral vanadium V2 site are detected for all samples, and those in the tetrahedral V1 site are additionally found for CVO:2.0Co. Disordering of O1, O4, O7 oxygen sites is observed in all structures. Combined results of X-ray diffraction analysis and X-ray absorption spectroscopy showed that the formal charge of Co ions is mixed between 2+ and 3+ with the prevalence of 2+. A trend towards a decrease in formal charge with an increase in Co concentration is observed. The coordination number of Co(2+δ)+ ions is found to be 4.6 and polyhedron is intermediate between tetrahedral and octahedral. The cobalt ions, having mixed formal charge Co(2+δ)+ and polyhedron between tetrahedral and octahedral, occupied Ca crystallographic sites, vacancies in the V sites, and disordering of oxygen sites are revealed in the Co-activated Ca 3 (VO 4) 2. [Display omitted] • Ca 3 (VO 4) 2 crystals doped with 0.1–2.0 ​wt % Co 3 O 4 were grown by Czochralski method. • Crystals were first studied by single-crystal X-ray diffraction and EXAFS/XANES. • The presence of Co in several Ca sites and vacancies in V sites were found. • Mixed formal charge (2+δ)+ with the prevalence of 2+ is revealed for Co. • The coordination number of Co(2+δ)+ ions is found to be 4.6. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca 3 (VO 4) 2 crystals doped with 0.1 and 1.0 wt.%Mn were grown by Czochralski method. • Crystals were first studied by single-crystal X-ray diffraction and EXAFS/XANES. • The presence of Mn3+ in several Ca2+ sites and vacancies in V5+ sites were found. • Mn3+ form elongated octahedron (tetragonal bipyramid) typical for Jahn-Teller ions. • Optical spectroscopy showed the presence of Mn3+ and low amounts of Mn2+ and Mn5+. Calcium orthovanadate Ca 3 (VO 4) 2 (CVO) is an efficient media for laser applications. Czochralski-grown green CVO single crystals doped with over-stoichiometric 0.1 (CVO:0.1Mn) and 1.0 wt.%Mn (CVO:1.0Mn) were studied by X-ray diffraction and X-ray absorption spectroscopy for the first time. In the CVO:1.0Mn, an occurrence of Mn3+ in Ca3 (two-capped trigonal prism), Ca4 (distorted octahedron), and defective Ca5 and Ca5 A (highly-distorted octahedron) sites and vacancies in V2 and V3 sites (distorted tetrahedra) were revealed. In the CVO:0.1Mn, a presence of Mn3+ in Ca3 and Ca5 A sites and vacancies in V2 site were found. In the CVO, the Mn3+ form elongated octahedra (tetragonal bipyramid; coordination number, 4 + 2) typical for the Jahn-Teller ions. Models for the rearrangement of Ca3 and Ca4 polyhedra into a tetragonal bipyramid are proposed. Along with the Mn3+, the Mn2+ and Mn5+ ions were observed by optical spectroscopy in CVO:0.1Mn (predominantly Mn2+ ions) and CVO:1.0Mn (only Mn5+ ions). [ABSTRACT FROM AUTHOR]