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The structure, oxygen non-stoichiometry, defect equilibrium, and thermodynamic properties of perovskite-type Pr 0.5 Ba 0.25 Sr 0.25 MnO 3– δ manganite were studied. It was shown that the manganite can be air synthesized in one step at 1450 °C. Though having a disordered arrangement of Pr, Ba, and Sr atoms, the compound crystallizes with a tetragonal structure (S.G. I 4 /mcm) due to the regular tilts of MnO 6 octahedra. The oxygen content in oxide as a function of oxygen partial pressure and temperature was measured by coulometric titration, and the data were used for the modeling of defect equilibrium. The oxygen content measurements show stability of the manganite at 973–1223 K and oxygen pressure decrease down to 10−16–10−12 atm. The equilibration of defects in Pr 0.5 Ba 0.25 Sr 0.25 MnO 3- δ involves oxygen exchange with the gaseous ambient, intrinsic electron excitation, and oxygen disordering reactions. According to thermodynamic calculations, oxygen sites available for oxygen exchange are characterized by praseodymium-rich coordination. The disordering caused by the half substitution of barium by strontium leads to a lower energy of chemical bonding of the labile oxygen in Pr 0.5 Ba 0.25 Sr 0.25 MnO 3– δ compared to the parent Pr 0.5 Ba 0.5 MnO 3– δ manganite. PrBa 0.5 Sr 0.5 Mn 2 O 6- δ was investigated in terms of structural features, phase stability, oxygen non-stoichiometry, defect equilibrium, and thermodynamic properties. [Display omitted] • The deep Sr doping in Pr 0.5 Ba 0.25 Sr 0.25 MnO 3– δ results in an enhanced phase stability. • PBSM crystallizes with tetragonal structure due to regular tilts of MnO 6 octahedra. • Oxygen sites available for exchange in PBSM are characterized by Pr-rich coordination. • The disordering in PBSM structure is caused by the half substitution of Ba by Sr. • Energy of chemical bonding of the labile oxygen in PBSM lower than in parent PBM. [ABSTRACT FROM AUTHOR]

The rare-earth germanium sulfide iodides RE 3 Ge 2 S 8 I (RE = La, Ce, Pr) have been prepared by reaction of the elements at 900 °C. They adopt the monoclinic La 3 (SiO 4) 2 Cl-type structure (space group C 2/ c , Z = 4; a = 16.156(4)–15.9760(9) Å, b = 7.9776(18)–7.8786(5) Å, c = 11.081(3)–10.9281(6) Å, β = 98.192(5)–98.4525(10)° on progressing from La to Pr for the RE component) consisting of isolated thiogermanate tetrahedral groups [GeS 4 ]4– separated by RE 3+ and I− ions. The optical band gaps fall in the range of 2.7–3.1 eV. Magnetic measurements indicated simple paramagnetic behaviour for Ce 3 Ge 2 S 8 I and Pr 3 Ge 2 S 8 I. Image 1 • Mixed-anion compounds RE 3 Ge 2 S 8 I were prepared for RE = La–Pr. • They contain RE 3+ cations, isolated thiogermanate units [GeS 4 ]4–, and I− anions. • Optical band gaps of 2.7–3.1 eV were measured. • The Ce and Pr members are paramagnetic down to 2 K. [ABSTRACT FROM AUTHOR]

Abstract Thermal quenching has been extensively regarded as one of the most significant challenges that limits the application of phosphors in today's world. Further effort is urgently required to understand the mechanism of thermal stability for achieving the improved performance of these phosphors. Sr 2 Ga 2 GeO 7 : Pr3+ has been synthesized by the conventional high temperature solid state reaction. A dominant green emitting is presented for the partial energy transition quenching process of the 3P 0 →3H 4 emission. The defect states structure is improved via the introducing of co-solvents, and the thermal stability of 1D 2 →3H 4 and 3P 0 →3H 4 levels can be further adjusted. The intervalence charge transfer (IVCT) and traps are introduced to explain the luminescence quenching properties of Sr 2 Ga 2 GeO 7 : Pr3+. The synergy of various models will provide a new idea for improving the luminescence stability of phosphors in the future. Graphical abstract With the increase of temperature, the thermal quenching temperature of 1D 2 and 3P 0 level is mainly due to the different effects of defects and IVCT on two levels. fx1 Highlights • The thermal stability mechanism of Sr 2 Ga 2 GeO 7 : Pr3+ needs to be further studied. • The introducing of co-solvents changes defect states structure. • The thermal stability of 1D 2 →3H 4 and 3P 0 →3H 4 levels is relative to IVCT and traps. [ABSTRACT FROM AUTHOR]

Abstract X-ray diffraction, crystal structure, magnetization, and heat capacity results are presented for the rare earth – chalcogenide ternary system PrCu 0.45 Te 2 and its non-4 f analogue LaCu 0.40 Te 2. The crystal structure of PrCu 0.45 Te 2 is characterized by chains of edge and corner-sharing CuTe 4 tetrahedra and Pr centered in polyhedra comprised of Cu and Te. The Cu site is partially occupied and exhibits signatures of local disorder. Magnetic susceptibility measurements show a Curie-Weiss temperature dependence consistent with a Pr3+ state. No magnetic ordering is observed down to 1.8 K, but the negative Curie-Weiss temperature suggests an antiferromagnetic exchange interaction. Importantly, the low temperature heat capacity of PrCu 0.45 Te 2 is strongly enhanced by comparison to LaCu 0.40 Te 2 , suggesting that there is a build-up of entropy that is associated with the 4f-electrons from the Pr3+ ions. These features reveal possible spin frustration behavior and introduce this family of materials as a template for studying new phenomenon. Graphical abstract fx1 Highlights • Single crystals of PrCu 0.45 Te 2 were grown in KI flux. • PrCu 0.45 Te 2 is composed of edge and corner-sharing CuTe 4 tetrahedra and Pr-centered polyhedra. • The Cu site is partially occupied and exhibits signatures of local disorder. • Low-temperature heat capacity measurements of PrCu 0.45 Te 2 reveal possible spin frustration behavior. [ABSTRACT FROM AUTHOR]

Abstract Praseodymium-containing double perovskites (Ba 1- x Sr x) 2 PrRuO 6 were prepared. They crystallize in a monoclinic structure with space group P 2 1 /n in the range of 0 ≤ x ≤ 0.30. Magnetic susceptibility measurements show that all these (Ba 1- x Sr x) 2 PrRuO 6 compounds order an antiferromagnetic transition at 95 ≤ T ≤ 117 K, and the Néel temperatures decrease with increasing Sr concentration (x value). Specific heat measurements and the magnetic entropy change for (Ba 1- x Sr x) 2 PrRuO 6 also reveal the simultaneous magnetic ordering of Pr and Ru ions. Graphical abstract Schematic crystal structures of double perovskite (Ba 1- x Sr x) 2 PrRuO 6. fx1 Highlights • Double perovskite (Ba 1- x Sr x) 2 PrRuO 6 were prepared in the range 0 ≤ x ≤ 0.30. • They have a monoclinic structure with space group P 21 /n. • These compounds show an antiferromagnetic ordering at 95–117 K. [ABSTRACT FROM AUTHOR]

Long persistent luminescence (LPL) phosphors have a wide range of potential applications, including multi-color anticounterfeiting and long-term continuous detection of short-wavelength ultra-violet (UV) radiation. However, developing a stable carrier container that can provide ultra-long carrier storage for activators and visible multi-color LPL is a challenging task. In this work, we presented a series of Pr3+-doped Y 3 GaO 6 (YGO) LPL phosphors that take full advantage of the synergistic relationship between the host lattice, emitters, and carrier traps. The host provides a suitable lattice site for rare-earth Pr3+ and offers a broad band gap of 5.69 eV to hold traps with depths ranging from 1.01 to 2.17 eV. We observed LPL that was visible to the naked eye for 6 h after excitation, and strong thermoluminescence (TL) spectra could be detected after the phosphor was placed in darkness for 20 days at room temperature. Additionally, we observed photostimulated luminescence under 980 nm and 808 nm laser irradiation with a power density of 5 W cm-2, indicating that low-energy excitation not only leads to LPL but also accelerates the elimination of previously stored carriers. After investigating the crystal structure and possible defects generated in the materials, we proposed a mechanism for LPL. Our findings demonstrate the potential of Pr3+-doped YGO LPL phosphors for a range of applications, such as multi-color anticounterfeiting and long-term continuous detection of short-wavelength UV radiation. [Display omitted] • Pr3+-doped Y 3 GaO 6 long persistent luminescence phosphors with trap depths ranging from 1.01 to 2.17 eV were designed. • The observed LPL that was visible to the naked eye for 6 h after excitation, and thermoluminescence could be detected after being placed in darkness for 20 days at room temperature. • The trap distribution was regulated by varying the Pr3+ concentration. • The photostimulated luminescence was detected under near-infrared laser irradiation. [ABSTRACT FROM AUTHOR]

Abstract CaSn(OH) 6 , CaSnO 3 and CaSnF 6 compounds were elaborated from a “one-batch” synthesis route: the coprecipitation of the pure double hydroxide leads to pure double oxide or fluoride after annealing treatments under air or HF as anhydrous gas, respectively. Structural and morphological features of the three matrices were carefully investigated by X Ray Diffraction analysis and Scanning Electron Microscopy, respectively. In addition, the luminescent properties of the Pr-doped compounds were performed and compared. The nanometric size of the double hydroxide inhibits the luminescence. The interpretation of the emission spectra obtained for Pr-doped CaSnO 3 and CaSnF 6 compounds is based on the covalence/ionic balance of the M–O or M–F bonds. Graphical abstract fx1 Highlights • Structural filiation of stannates compounds. • 119Sn Mossbauer analysis of Sn-X chemical bonding (X = OH, O, F). • Nephelauxetic effect observed in the luminescence of Pr3+ doped stannate compounds. [ABSTRACT FROM AUTHOR]

Combustion synthesized La 2 O 3 , La 2-2x Pr 2x O 3 (x = 0.025–0.30), La 2-2x Nd 2x O 3 (x = 0.025–0.50), La 2-2x Sm 2x O 3 (x = 0.025–0.30) and their subsequently formed hydroxide phases were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The hydroxylation reaction (hygroscopic property) of oxides in an open atmosphere was monitored by X-ray diffraction (XRD). All of these oxides hydroxylate to form stable hydroxides at room temperature upon exposure to open atmosphere for certain interval of time. La 2 O 3 shows rapid hydroxylation reaction as compared to other oxides (La 2-2x M 2x O 3 , M = Pr, Nd, Sm). It is observed that La 2-2x Pr 2x O 3 shows the slowest hydroxylation reaction compared to La 2-2x Nd 2x O 3 and La 2-2x Sm 2x O 3 . Further, as the concentration of dopant ion concentration increases in each La 2-2x Pr 2x O 3 (x = 0.05, 0.15 and 0.30), La 2-2x Nd 2x O 3 (x = 0.05, 0.15, 0.30 and 0.50) and La 2-2x Sm 2x O 3 (x = 0.05, 0.15 and 0.30), the hydroxylation reaction becomes slower consecutively. Overall, 30% Pr doped La 2 O 3 (La 1.40 Pr 0.60 O 3 ) shows the highest stability (slowest rate of hydroxylation) in open atmosphere at room temperature. [ABSTRACT FROM AUTHOR]

Praseodymium-containing cobalt perovskites, such as (Pr 1−y Y y ) 1−x Ca x CoO 3-δ , have been argued to undergo a first-order charge shift between Pr and hybridized Co-O orbitals that leads to a metal-insulator transition at a temperature, T VT . Magnetization and x-ray absorption spectroscopy measurements on single crystals of (Pr 0.85 Y 0.15 ) 0.7 Ca 0.3 CoO 3-δ grown in an IR image furnace under 40–60 bar of oxygen confirm the presence of this valence transition. Single crystal x-ray synchrotron diffraction measurements are consistent with an isomorphic phase transition at T VT . No evidence of charge ordering was revealed by the single crystal diffraction. Dissimilar to analytical transmission electron microscopy measurements performed on a grain from a polycrystalline sample that revealed an oxygen vacancy order-disorder transition at T VT , the present single-crystal measurements did not evidence such a transition, likely reflecting a lower density of oxygen vacancies in the high-pO 2 grown single crystals. [ABSTRACT FROM AUTHOR]

A new double perovskite Pr 2 CoTiO 6 has been synthesized by conventional solid state method. The structure of the compound has been investigated through powder x-ray and neutron diffraction techniques. The Rietveld refinement of the structural data shows that the compound crystallizes in the monoclinic structure (S.G. P 2 1 / n # 14)). The refined cell parameters are: a = 5.4800(6) Å , b = 5.6221(6) Å, c = 7.7700(9) Å, β = 89.98(4)°. Monoclinic distortion ϕ associated with the distortion of the CoO 6 - and TiO 6 - octahedra is 13.7°. Magnetic measurements down to 4 K show antiferromagnetic-like ordering of the material, T N ~ 17 K with paramagnetic effective magnetic moment μ eff = 6.92 μ B . At room temperature, the dielectric constant and dielectric loss of Pr 2 CoTiO 6 are 45.5 and 1.2 respectively. [ABSTRACT FROM AUTHOR]

Solid solutions Pr 3 (Ru 1- x Ta x )O 7 (0≤ x ≤1.0) and (Pr 1- x Y x ) 3 RuO 7 (0≤ x ≤0.7) were obtained as a single phase compound. They crystallize in an orthorhombic superstructure derived from that of the cubic fluorite with space group Cmcm . The results of the Rietveld analysis for X-ray diffraction profiles of Pr 3 (Ru 1- x Ta x )O 7 showed that Ru and Ta atoms are randomly situated at the six-coordinate 4 b site. For (Pr 1- x Y x ) 3 RuO 7 , with increasing the concentration of Y ions ( x value), the smaller Y ions occupy selectively the seven-coordinate 8 g site rather than the eight-coordinate 4 a site. Through magnetic susceptibility measurements for Pr 3 (Ru 1- x Ta x )O 7 , the antiferromagnetic transition temperatures decrease linearly with increasing x value, and at x =0.75 no magnetic ordering was found down to 1.8 K, indicating the magnetic interaction is not one-dimensional, but three-dimensional. On the other hand, the antiferromagnetic transition temperature for (Pr 1- x Y x ) 3 RuO 7 decreases with increasing x value, but above x ≥0.50 it becomes constant (~12 K). This result indicates that Pr 3+ ions at the seven-coordinate site greatly contribute to the antiferromagnetic interactions observed in (Pr 1- x Y x ) 3 RuO 7 . Density functional calculations of Pr 3 RuO 7 demonstrate that the electronic structure gives insulating character and that oxygen 2p orbitals hybridize strongly with Ru 4d orbitals in the valence band (VB). Near the top of VB, the Pr 4 f orbitals at the seven-coordinated site also show a weak hybridization with the O(1) 2p orbitals. The Ru-O(1)-Pr superexchange pathway take part in three-dimensional magnetic interaction and play an important role in an enhancement of long-range magnetic ordering. [ABSTRACT FROM AUTHOR]

The double perovskite praseodymium cobaltite lightly doped with yttrium Pr 0.9 Y 0.1 BaCo 2 O 6– δ (PYBCO) was obtained by combustion of organo-metallic precursors and shown to have a tetragonal structure with the crystalline lattice parameters a = b =3.903 and c =7.621 Å. The PYBCO composition occurs remarkably stable as show coulometric titration measurements of oxygen content (6– δ ) in the oxygen pressure range 10 –13 –0.21 atm and at temperatures variations within 650–950°С. The experimental data were utilized in order to derive partial thermodynamic functions of oxygen that govern equilibration of defects in PYBCO. The oxygen partial enthalpy Δ H ¯ O ( δ ) and entropy Δ S ¯ O ( δ ) both experience strong changes near (6– δ )=5. The observed behavior of Δ H ¯ O ( δ ) and Δ S ¯ O ( δ ) is explained in frameworks of the defect formation model, which involves reactions of charge disproportionation of Co 3+ cations, oxygen exchange with the gas phase and oxygen disordering over O2 and O3 structural positions. The verification of the suggested approach is carried out by comparison with independently obtained thermochemical data. [ABSTRACT FROM AUTHOR]

Compared with other traditional proton-conducting materials, the structures of metal-organic frameworks (MOFs) are more advantageous in terms of designability and tunability. Considering the strong and flexible coordination ability of carboxylate-based thiourea ligands, we synthesized a [3-(naphthalene-2-carbonyl)-thioureido]-acetic acid (H 3 L) ligand, and successfully obtained {[Pr(H 2 L) 2 (NO 3)(H 2 O) 2 ]·2H 2 O·MeOH} n (1). 1 is a 1D framework, in which the Pr(III) atoms are bridged by carboxyl oxygen, and then form a three-dimensional solid-state structure under the action of intermolecular hydrogen bonds and π-π stacking interactions. AC impedance measurements uncover that proton conductivity (σ) of 1 has a significant positive temperature and humidity dependence. The σ of MOF 1 can attain 3.41 ​× ​10−4 ​S/cm under 100 ​°C and 98% RH. In addition, the proton-conductive mechanism was discussed based on the structural analysis, H 2 O vapor adsorption curve and the activation energies evaluated by fitting the Arrhenius equation. [Display omitted] • One highly thermal-stable MOF from a naphthyl acylthiourea-carboxylate ligand was prepared. • The proton conductivity was examined at variable RHs and temperatures. • The proton-conducting mechanism was highlighted. [ABSTRACT FROM AUTHOR]

Double perovskite oxides of the A 2 B'B″O 6 type with Jahn-Teller active Cu2+ as the B′ constituent have gained considerable research interest in recent years. For fundamental studies, the rare earth element (R) based systems such as R 2 CuTiO 6 form an intriguing research platform as they allow systematic chemical-pressure studies by simply controlling the size of the R constituent. However, for the R 2 CuTiO 6 compounds conventional ambient-pressure high-temperature synthesis yields an orthorhombic (Pnma) double perovskite structure for the largest R constituents (La–Gd) only, while the compounds with the smaller R :s adopt a hexagonal structure. Here we demonstrate a hexagonal-to-perovskite structure conversion for the R ​= ​Y compound achieved through a high-pressure (HP) high-temperature treatment at 4 ​GPa and 1000 ​°C. Structural details of the thus stabilized new double perovskite phase of Y 2 CuTiO 6 are addressed through a combined DFT simulation and Rietveld refinement study, revealing signs towards the rare layered-type ordering of the B-site (Cu and Ti) cations. Similar to the previously reported R 2 CuTiO 6 perovskite phases with R ​= ​La, Pr, and Nd, the R ​= ​Y member is found paramagnetic throughout the measured temperature range of 5–300 ​K. From UV–vis absorption measurements the optical bandgap is estimated to be ca 3.4 ​eV. With high pressure treatment at 4 ​GPa and 1000 ​°C, hexagonal Y 2 CuTiO 6 can be transformed into orthorhombic perovskite. This extends the known R 2 CuTiO 6 (R ​= ​La–Gd) perovskite family to considerably smaller rare earth element (R) constituents and allows new properties to be discovered: here, partial layer-type B-site order which is rare for perovskites. [Display omitted] • Hexagonal Y 2 CuTiO 6 is converted to orthorhombic perovskite via high pressure treatment. • This extends the R 2 CuTiO 6 perovskite series (R ​= ​La–Gd) to the smaller R s. • Combined Rietveld and DFT analysis points towards partial layer-type B-site order. • Magnetic measurement shows paramagnetic behaviour down to 5 ​K. • Strongly negative Weiss temperature indicates antiferromagnetic spin interactions. [ABSTRACT FROM AUTHOR]

New fluorite-related quaternary rare earth oxides Pr 2 YRuO 7 and La 2 TbRuO 7 have been prepared. They crystallize in an orthorhombic superstructure of cubic fluorite with space group Cmcm . Through magnetic susceptibility and specific heat measurements, Pr 2 YRuO 7 shows an antiferromagnetic transition at 27 K, which is considerably lowered compared with that for Pr 3 RuO 7 . Analysis of the magnetic specific heat indicates that the magnetic behavior observed at 27 K for Pr 2 YRuO 7 is predominantly due to the magnetic interactions between Ru ions, and that the interactions between the Pr 3+ and Ru 5+ ions are also important. La 2 TbRuO 7 shows magnetic ordering at 9.0 K, which is ascribed to the magnetic ordering between Ru 5+ ions from the analysis of the magnetic specific heat data. [ABSTRACT FROM AUTHOR]

Pr 1.33 Pt 4 Ga 10 crystals were prepared by Ga-flux method. The superstructure of this compound was studied by single-crystal X-ray diffraction (XRD), transmission electron microscopy (TEM), and diffuse X-ray scattering. Pr 1.33 Pt 4 Ga 10 adopts the P 6 3 / mmc space group with a = b =4.3227(5) Å, c =16.485(3) Å: the structure features Pr 2 Ga 3 layers alternating with Pt 2 Ga 4 layers along the c -axis. TEM studies and pair distribution function (PDF) analysis of X-ray total scattering data show that Pr 2 Ga 3 layers possess an ordered superstructure (of dimension a ′ = a 3 ) in which Pr vacancies and Ga atoms are ordered within the ab -plane but disordered along the c -direction. PDF analysis also shows temperature-dependent structural features local to the Pr 3+ ion. Magnetic measurements reveal that Pr 3+ ions order ferrimagnetically below 12.5(2) K. [ABSTRACT FROM AUTHOR]

Abstract: Structural, electrical and magnetic properties of the layered cobaltite PrBa0.5Sr0.5Co2O5+δ have been investigated by means of neutron diffraction, electron diffraction, thermogravimetric analysis and SQUID magnetometry. Rietveld analysis of neutron diffraction data shows the ordered distribution of oxygen vacancies in [PrO δ ] planes which doubles the lattice parameters from the simple perovskite cell parameter as a≈2a p and c≈2a p (a p is the cell parameter of the simple Perovskite) yielding tetragonal symmetry in the P4/mmm space group. On heating, above 573K in air, structural rearrangement takes place and the structure can be defined as a≈a p and c≈2a p in the same space group. Oxygen occupancies have been determined as a function of temperature from neutron diffraction results. Initially (≥373K), oxygen occupancy was increased and then decreased with increasing temperature. It was found that at 973K the total oxygen loss is calculated about 0.265 oxygen/formula unit. Oxygen vacancy ordering was observed below 573K, and the oxygen occupancy decreases as cell volume increases with increasing temperature. Area specific resistance (ASR) measurements show a resistance of 0.153Ωcm2 and 0.286Ωcm2 at 973K and 923K, respectively. On cooling, paramagnetic to ferromagnetic and an incomplete ferromagnetic to antiferromagnetic transition takes place. Different behaviours in field cooled and zero-field-cooled measurements leads to a coexistence of ferromagnetic and antiferromagnetic order. [Copyright &y& Elsevier]

Abstract: The coulometric titration data are utilized in order to calculate changes of oxygen partial entropy and enthalpy in with variations of oxygen content and temperature. The thermodynamic equilibrium of the cobaltite with the ambient gas phase is analyzed based on the interface of oxygen exchange and oxidation, and the intrinsic reaction of thermal excitation of Co3+ cations. The partial thermodynamic functions of the movable oxygen in are shown to be interrelated with the thermodynamic parameters of the defect formation reactions. The existence of a band gap of about 0.4eV in the electronic spectrum of the cobaltite follows from a favorable comparison of the calculated and experimental dependencies of the partial thermodynamic functions of the movable oxygen. [Copyright &y& Elsevier]

A new rare earth based double perovskite oxide barium praseodymium cobalt niobate, BaPrCoNbO6 (BPCN) is synthesized by solid-state reaction technique. Rietveld analysis of X-ray diffraction (XRD) data shows that the compound crystallizes in a perovskite like tetragonal structure which belongs to the I4/mmm space group with lattice parameters a=b=5.6828(9)Å, c=8.063(2)Å. Structural analysis reveals 1:1 ordered arrangement for the Co2+ and Nb5+ cations over the six-coordinate B-sites of BPCN. The superlattice line (101) at 2θ=19.10° arising from the alternate ordering of Co2+ and Nb5+ sites is observed in the XRD pattern which confirms the presence of cation ordering in BPCN. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO6 stretching vibration. The relaxation dynamics of the conductive process in BPCN is investigated in the temperature range 303 to 503K and in the frequency range 100Hz to 1MHz using impedance spectroscopy. The relaxation mechanism of the sample in the framework of electric modulus formalism is modeled by Davidson–Cole model (DCM). The values of α (distribution of relaxation time) for the DCM varies from 0.1 to 0.3 which suggests the asymmetric distribution of relaxation time for BPCN. The activation energy of the sample, calculated from both conductivity and modulus spectra, are found to be almost the same ~0.4eV, which indicates that the conduction mechanism for BPCN is polaron hopping. The scaling behaviour of the imaginary part of electric modulus suggests that the relaxation follows the same mechanism at various temperatures. [ABSTRACT FROM AUTHOR]

A defect equilibrium model for PrBaCo2O5+δ is suggested based on oxygen non-stoichiometry data. The model includes reactions of oxygen exchange and charge disproportionation of Co3+ cations. The respective equilibrium constants, enthalpies and entropies for the reactions entering the model are obtained from the fitting of the experimental data for oxygen non-stoichiometry. The enthalpies of oxidation Co2+→Co3+ and Co3+→Co4+ are found to be equal to 115±9kJmol–1 and 45±4kJmol–1, respectively. The obtained equilibrium constants were used in order to calculate variations in concentration of cobalt species with non-stoichiometry, temperature and oxygen pressure. [ABSTRACT FROM AUTHOR]

Doping a hybrid perovskite semiconductor with metal elements offers an effective means of adjusting its photoelectric properties. To give one example, it has been found that adding lanthanide elements such as Europium (Eu) and Samarium (Sm) into a perovskite layer enhances the photovoltaic performance and photothermal stability of perovskite solar cells. In this study, we therefore added different Praseodymium (Pr)/Lead (Pb) ratios from 0% to 1% to perovskite films in a precursor solution of tri-cation perovskite. We found the photoelectric properties and device performance of perovskite solar cells doped with 0.25% Praseodymium ion (Pr3+) to be significantly improved, with a champion power conversion efficiency (PCE) of 18.56% obtained. Furthermore, the stability of perovskite solar cells (PSCs) with 0.25% Pr3+ doping improved effectively. Overall, with Pr3+ doping, the carrier mobility was dramatically enhanced, and the carrier recombination effectively hindered. These results therefore indicate that Pr3+ doping causes the perovskite to produce lattice shrinkage. As such, the findings shed light on a fresh dopant engineering tactic for fabricating high performance perovskite solar cells. [Display omitted] • Via praseodymium ions (Ⅲ) doping, the perovskite film exhibited excellently enhanced carrier extraction ability. • The PCE of praseodymium chloride doped PSC were improved with better fill factor. • The stability of PSCs was greatly improved by praseodymium ions (Ⅲ) doping. [ABSTRACT FROM AUTHOR]

Abstract: Four antimony-containing pyrochlores with compositions Bi2−x Fe x (FeSb)O7, where x=0.1, 0.2, 0.3, and Nd1.8Fe0.2(FeSb)O7 have been synthesised, their structural properties examined, and compared to that of the pyrochlore phase Pr2(FeSb)O7 which we have structurally characterised for the first time. The Fe3+ ions in Pr2(FeSb)O7 are located only on the B-sites whereas in the bismuth- and neodymium-containing pyrochlore structures the Fe3+ ions are present on both the A- and B-sites giving rise to static displacive disorder in the A 2O'' chains. The presence of a smaller cation on the A-site in materials of composition Bi2−x Fe x (FeSb)O7 appears to lower the radius ratio (r A/r B) and leads to a stabilisation of the structure. Magnetic susceptibility measurements reveal no long range order, but Bi1.9Fe0.1(FeSb)O7 and Bi1.8Fe0.2(FeSb)O7 undergo transitions at ca. 12K to a spin-glass state; Nd1.8Fe0.2(FeSb)O7 and Pr2(FeSb)O7 are paramagnetic. [Copyright &y& Elsevier]

Abstract: Crystal growth and full structure determination of compounds adopting the CeCr2Al20 structure type, LnTi2Al20 (Ln=La–Pr, Sm, and Yb), LnV2Al20 (Ln=La–Pr, and Sm), and LnCr2Al20 (Ln=La–Pr, Sm, and Yb), are reported. Resistivity, magnetic susceptibility, and heat capacity of flux grown single crystals of the nonmagnetic CeM2Al20 (Ln=Ce, Yb; M=Ti, V) compounds are compared to PrCr2Al20. Of particular interest is PrCr2Al20 which does not show any phase transition down to the lowest temperature of the measurement (400mK in resistivity measurement and 1.8K for magnetic susceptibility measurements) and exhibits Kondo behavior at low temperatures. [Copyright &y& Elsevier]

Abstract: The spectroscopic parameters and electronic structure of binary titanate Pr2Ti2O7 have been studied by IR-, Raman and X-ray photoelectron spectroscopy (XPS) for the powder sample prepared by solid state synthesis. The spectral features of valence band and all constituent element core levels have been considered. The Auger parameters of titanium and oxygen in Pr2Ti2O7 have been determined as α Ti=872.8 and α O=1042.3eV. Variations of cation–anion bond ionicity have been discussed using binding energy differences ΔTi=(BE O 1s–BE Ti 2p3/2)=71.6eV and ΔPr=BE(Pr 3d5/2)−BE(O 1s)=403.8eV as key parameters in comparison with those of other titanium- and praseodymium-bearing oxides. [Copyright &y& Elsevier]

Abstract: The luminescence properties of CaMoO4:Pr3+ have been investigated in different experimental conditions in order to obtain information on the excitation and de-excitation pathways of this system. The structure of the emission spectrum depends on different factors: excitation conditions, doping level, temperature, etc. In addition, measurements carried out on single crystals and on micro- or nano-crystalline powders obtained by solid state reaction and sol–gel method have revealed that the morphology of the sample, and then the concentration of the lattice defects, strongly influences the excitation mechanism. These effects have been analysed in the light of available models and a general scheme accounting for the experimental observations has been proposed. [Copyright &y& Elsevier]

Abstract: Kinetic lattice Monte Carlo (KLMC) model is developed for investigating oxygen vacancy diffusion in praseodymium-doped ceria. The current approach uses a database of activation energies for oxygen vacancy migration, calculated using first-principles, for various migration pathways in praseodymium-doped ceria. Since the first-principles calculations revealed significant vacancy–vacancy repulsion, we investigate the importance of that effect by conducting simulations with and without a repulsive interaction. Initially, as dopant concentrations increase, vacancy concentration and thus conductivity increases. However, at higher concentrations, vacancies interfere and repel one another, and dopants trap vacancies, creating a “traffic jam” that decreases conductivity, which is consistent with the experimental findings. The modeled effective activation energy for vacancy migration slightly increased with increasing dopant concentration in qualitative agreement with the experiment. The current methodology comprising a blend of first-principle calculations and KLMC model provides a very powerful fundamental tool for predicting the optimal dopant concentration in ceria related materials. [Copyright &y& Elsevier]

Abstract: Properties of LaAlO3 nanocrystallites obtained by the precipitation method, doped with praseodymium and chromium ions were examined by spectroscopic means. Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and electronic spectroscopy proved that symmetry of LaAlO3 crystallites depends on their size. At room temperature the smallest obtained crystals (average size ∼5nm) have cubic symmetry, while the largest ones (average size over 110nm) exhibit rhombohedral symmetry. Possible explanations for this phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Oxypnictides of the type PrOFe1− x Co x As (x≤0.3) were synthesized for the first time by the sealed tube method. All the compounds were found to be monophasic and crystallize in the tetragonal ZrCuSiAs type structure (space group=P4/nmm) and the lattice parameters (a and c) decrease with increase in cobalt content. Mössbauer measurements of the compounds indicate low spin Fe2+ in tetrahedral coordination. Resistivity and magnetization studies reveal superconducting transitions in compounds with ‘x’=0.05, 0.10 and 0.15, with maximum transition temperature (Tc ) at ∼14K in the compound with ‘x’=0.1. The variation of resistivity with temperature under different magnetic field has been studied to estimate the upper critical field (Hc 2) (∼50.2T for the ‘x’=0.1 composition). The Seebeck and Hall coefficient (RH ) suggests electron type charge carriers in these compound and the charge carrier density increases with increase in Co-doping. [Copyright &y& Elsevier]

Abstract: The luminescence properties of KLa(MoO4)2 (KLM) single crystals doped with Pr3+ have been measured in the 10–600K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr3+, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr3+ levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb3+-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases. [Copyright &y& Elsevier]

Abstract: Pr3+-doped perovskites R 1/2Na1/2TiO3:Pr (R=La, Gd, Lu, and Y) were synthesized, and their structures, optical absorption and luminescent properties were investigated, and the relationship between structures and optical properties are discussed. Optical band gap of R 1/2Na1/2TiO3 increases in the order R=La, Gd, Y, and Lu, which is primarily due to a decrease in band width accompanied by a decrease in Ti–O–Ti bond angle. Intense red emission assigned to f–f transition of Pr3+ from the excited 1D2 level to the ground 3H4 state upon the band gap photo-excitation (UV) was observed for all compounds. The wavelength of emission peaks was red-shifted in the order R=La, Gd, Y, and Lu, which originates from the increase in crystal field splitting of Pr3+. This is attributed to the decrease in inter-atomic distances of Pr–O together with the inter-atomic distances (R, Na)-O, i.e., increase in covalency between Pr and O. The results indicate that the luminescent properties in R 1/2Na1/2TiO3:Pr are governed by the relative energy level between the ground and excited state of 4f 2 for Pr3+, and the conduction and valence band, which is primarily dependent on the structure, e.g., the tilt of TiO6 octahedra and the Pr-Ti inter-atomic distance and the site symmetry of Pr ion. [Copyright &y& Elsevier]

Abstract: High-pressure chemistry led to the synthesis of the rare-earth borate Pr4B10O21 using a Walker-type multianvil apparatus at 3.5GPa and 1050°C. The tetra-praseodymium(III)-decaborate crystallizes monoclinicly with four formula units in the space group P21/n and lattice parameters of a=710.2(2), b=1948.8(4), c=951.6(2)pm, and β=93.27(3)°. The boron–oxygen network consists of [BO4]5− tetrahedra and [BO3]3− groups; however, the [BO4]5− groups represent the major part (80%) due to the high-pressure conditions during the synthesis. The praseodymium ions are coordinated by 10 and 12 oxygen atoms. Along with a detailed description of the crystal structure, temperature programmed X-ray powder diffraction data are shown, demonstrating the metastable character of this compound. [Copyright &y& Elsevier]

Abstract: CaIn2O4:Dy3+/Pr3+/Tb3+ blue–white/green/green phosphors were prepared by the Pechini sol–gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), diffuse reflectance, photoluminescence (PL) and cathodoluminescence (CL) spectra as well as lifetimes were utilized to characterize the samples. The XRD results reveal that the samples begin to crystallize at 800°C and pure CaIn2O4 phase can be obtained after annealing at 900°C. The FE-SEM images indicate that the CaIn2O4:Dy3+, CaIn2O4:Pr3+ and CaIn2O4:Tb3+ samples consist of spherical grains with size around 200–400nm. Under the excitation of ultraviolet light and low-voltage electron beams (1–5kV), the CaIn2O4:Dy3+, CaIn2O4:Pr3+ and CaIn2O4:Tb3+ phosphors show the characteristic emissions of Dy3+ (4F9/2–6H15/2 and 4F9/2–6H13/2 transitions, blue–white), Pr3+ (3P0–3H4, 1D2–3H4 and 3P1–3H5 transitions, green) and Tb3+ (5D4–7F6,5,4,3 transitions, green), respectively. All the luminescence is resulted from an efficient energy transfer from the CaIn2O4 host lattice to the doped Dy3+, Pr3+ and Tb3+ ions, and the corresponding luminescence mechanisms have been proposed. [Copyright &y& Elsevier]

Abstract: Thermochemical investigations have been carried out to elucidate the phase relationships in the system Pr2Se3–PrSe2 and to construct the p Se–T–x diagram. The result of the tensimetric and thermogravimetric studies showed the thermal decomposition of PrSe2 to be a step-wise process due to the formation of a sequence of discrete intermediate phases with the compositions PrSe1.9, PrSe1.85, PrSe1.8, and Pr2Se3. PrSe1.85 and PrSe1.8 have been previously considered as selenium-deficient non-stoichiometric phases. Conclusions derived from the thermodynamic study were verified by X-ray diffraction and electron microscopy studies on single crystals of PrSe1.85 which were obtained from reactions of praseodymium and selenium in stoichiometric amounts in a KCl flux at 1070K. A two-dimensional modulation could be observed for PrSe1.85 in X-ray and high-resolution transmission electron microscopy. The structure of PrSe1.85 was solved and refined in superspace group P4/n()(β–α )00 with lattice parameters of a=4.137(1)Å, c=8.398(2)Å of the basic unit cell and α=β=0.293(1). The origin of the modulation can be attributed to a site occupancy wave and a charge density wave in its planar selenium layer. The experimentally determined magnetic moments indicate Pr3+ for the polyselenides PrSe2, PrSe1.9 and PrSe1.85. [Copyright &y& Elsevier]

Abstract: With a view to investigate the effect of small size of A-site cations on the magnetic properties of the rare earth cobaltates, Ln 1− xAx CoO3 (Ln=rare earth, A=alkaline earth), we have investigated Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3 in detail. For this purpose, we have carried out low-field DC magnetization and ac susceptibility measurements including a study of magnetic relaxation and memory effects. Both Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3 show frequency-dependent transitions at 70 and 55K respectively in the ac susceptibility data, due to the onset of spin-glass like behavior. Their relaxation behavior exhibits aging effects. In addition, memory effects are found in the magnetization behavior. These characteristics establish spin-glass behavior in both these cobaltates, a behavior that is distinctly different from that of La0.7Ca0.3CoO3 and La0.5Sr0.5CoO3 which show well-defined ferromagnetic transitions, albeit without long-range ordering. [Copyright &y& Elsevier]

Abstract: The praseodymium cobalt aluminides, PrCo2Al8 and Pr2Co6Al19, were prepared by reaction of the elemental components in an arc-melting furnace, followed by heat treatment at 900°C for several days. Their chemical composition was checked by scanning electron microscopy and energy dispersive spectroscopy, and their crystal structure was refined from single crystal X-ray diffraction data. PrCo2Al8 adopts the CaCo2Al8 type of structure, crystallizing with the orthorhombic space group Pbam, with four formula units in a cell of dimensions at room temperature: , , . Pr2Co6Al19 crystallizes in the monoclinic space group C2/m, with four formula units in a cell of dimensions at room temperature: , , and . Its structure belongs to the U2Co6Al19 type. The crystal structures of both compounds studied can be viewed as three-dimensional structures resulting from the packing of Al polyhedra centred by the transition elements. Along the c-axis, the coordination polyhedra around the Pr atoms pack by face sharing to form strands, which are separated one from another by an extended Co–Al network. Magnetic measurements have revealed that PrCo2Al8 orders antiferromagnetically at , with a clear metamagnetic transition occurring at a critical field H c=0.9(1)T. The temperature dependence of the susceptibility of Pr2Co6Al19 does not provide any evidence for long-range magnetic ordering in the temperature domain 1.7–300K. At low temperatures (T<10K), the susceptibility saturates in a manner characteristic of a non-magnetic singlet ground state. At high temperatures, the magnetic susceptibility of each compound follows a Curie–Weiss law, with the effective magnetic moment per Pr atom of 3.48(5)μ B and 3.41(2)μ B for PrCo2Al8 and Pr2Co6Al19, respectively. These values are close to the theoretical value of 3.58μ B expected for a free Pr3+ ion and exclude any contribution due to the Co atoms. Both compounds exhibit in the temperature range 5–300K metallic-like electrical conductivity, and their Seebeck coefficient is of the order of several μV/K. [Copyright &y& Elsevier]

Abstract: The isotypic oxonitridosilicate chlorides Ln 4[Si4O3+ x N7− x ]Cl1− x O x with Ln=Ce, Pr, Nd and were obtained by the reaction of the respective rare-earth metals, their oxides and chlorides with “Si(NH)2” in a radiofrequency furnace at temperatures around 1800°C, using CsCl as a flux. The crystal structures were determined by single-crystal X-ray diffraction (, no. 198, , Ce: , ; Pr: , ; Nd: , ) and found to be isotypic with Ce4[Si4O4N6]O. In order to characterize the incorporation of chlorine into the structure, the crystallographic site occupation factors of O, N and Cl were determined by neutron powder diffraction. Furthermore, these results were substantiated by the chemical analyses for Pr4[Si4O3+ x N7− x ]Cl1− x O x and electron microphobe analyses for all of the synthesized oxonitridosilicate chlorides. Temperature-dependent magnetic susceptibility measurements of the cerium and the praseodymium compound indicate Curie–Weiss behavior with experimentally determined magnetic moments of 2.15(5) μ B/Ce and 3.50(5) μ B/Pr, respectively. No magnetic ordering could be detected down to 2K. The 4f 1 of cerium has been confirmed by XAS measurements. [Copyright &y& Elsevier]

Abstract: The interpretation of the spectra of free atoms and gaseous ions in the 4fN and 5fN periods became less active after critical compilations of energy levels appeared. However, several spectra are still under study and the application of the Racah–Slater and HFR methods to extended sets of configurations leads to revisions and additions. In doubly charged ions of lanthanides, the treatment of configuration interaction by means of effective parameters and by extension of the basis of states are both important. Concerning actinides, calculations of several observables (Landé factors and isotope shifts in Pu I, hyperfine constants, transition probabilities) prove the quality of eigenfunctions. The classification of Es I and Es II has been extended and radial parameters for fine and hyperfine structures have been derived. Level predictions for the next element fermium are supported by parameter extrapolations. [Copyright &y& Elsevier]

Magnetic and calorimetric properties of Ln3RuO7 (Ln=Pr, Gd) have been investigated. Magnetic susceptibility and specific heat measurements indicate that both Pr3RuO7 and Gd3RuO7 compounds show magnetic transitions at 55 K and 15 K, respectively. In addition, a clear structural phase transition has been found at 382 K for Gd3RuO7 from the specific heat measurements. From the temperature dependence of the magnetic specific heat, the magnetic entropy change is estimated and the magnetic ground states of each ion are determined. [ABSTRACT FROM AUTHOR]

This study relates structure, properties and thermodynamics, through synthesis, characterization and heat of formation measurements of rare earth iridate pyrochlore (RE 2 Ir 2 O 7 ; RE ​= ​Y, Eu, Pr) crystalline powders. The RE 2 Ir 2 O 7 phases are synthesized by high temperature solid-state synthesis methods. X-ray diffraction and elemental analysis techniques are utilized to validate the synthesis and enable structural comparisons. Trends in the bond angles indicate deviations from the Y and Eu analogs for the Pr 2 Ir 2 O 7 phase. High temperature oxide melt solution calorimetry is used to determine the heats of formation of each phase. Breaking the trend expected across the rare earth series, the enthalpy of formation for Pr 2 Ir 2 O 7 is more exothermic than the anticipated from the Y and Eu analogs. Rare earth (RE ​= ​Y, Eu, Pr) iridate pyrochlores phases are synthesized by high temperature solid-state synthesis methods. Structure – property relationship studies identify uniqueness of each analog. [Display omitted] • The synthesis, characterization and heat of formation measurements of rare earth iridate pyrochlore (RE 2 Ir 2 O 7 ; RE ​= ​Y, Eu, Pr) crystalline powders. • High temperature oxide melt solution calorimetry is used to determine the heats of formation of each phase. • The enthalpy of formation for Pr 2 Ir 2 O 7 ​is more exothermic than the anticipated. [ABSTRACT FROM AUTHOR]

Praseodymium doped zirconium silicate pigments (Pr x Zr 1-x SiO 4) were synthesized by a solid-state reaction, and the influence of praseodymium fraction (x ​= ​0.03, 0.05 or 0.07), temperature (900, 1000, 1100 or at 1200 ​°C) and calcination time (6, 12, 24 or 48 ​h) was simultaneously tested to determine their effect on colorimetric properties. The chromatic properties are associated with the volume of the unit cell; thus, with the amount of Pr4+ that is integrated into the crystal structure, the ascending concentration of the Pr4+ into zircon structure increases the color intensity only in the range where the unit cell volume is close to 261 ​Å3, lower or higher values result in pigments with lower yellow intensities. An intense reddish-yellow tone can be reached delimited by praseodymium fraction of 0.03 and 0.05, temperature between 900 and 1100 ​°C, and 6 ​h of calcination time. [Display omitted] • Pr4+ into zircon structure increases the color intensity if the unit cell volume is close to 261 ​Å3. • An intense reddish-yellow tone can be reached delimited by praseodymium fraction of 0.03 and 0.05 • An intense reddish-yellow tone can be reached between 900 and 1100 ​°C. • An intense reddish-yellow tone can be reached at 6 ​h of calcination time. • Pigment green tone increases if is synthesized with high calcination time and temperature and high praseodymium fraction. [ABSTRACT FROM AUTHOR]

Present herein is a new structure type of lanthanide-doped polyoxotitanium (Ln-POT) involving the separation of the polyoxotitanium and lanthanide clusters. A unique cocrystallization is observed in the structure of H 6 [Ti 12 (O i Pr) 18 (μ 3 -O 14)][La 3 (NO 3) 11 (O i Pr) 6 ] (1). Diffuse reflectance spectroscopy showing lanthanide doping is shown to give favorable light absorption properties. The report herein is a unique structure type of lanthanide-doped polyoxotitanium H 6 [Ti 12 (O i Pr) 18 (μ 3 -O 14)][La 3 (NO 3) 11 (O i Pr) 6 ]. It represents the first example involving the separation of the polyoxotitanium and lanthanide constituents. Image 1 • Present here is a new structure type of lanthanide doped polyoxotitanium (Ln-POT). • A cocrystallization of polyoxotitanium cages with lanthanide clusters is observed. • The temperature has a great influence on the structure type of Ln-POT. [ABSTRACT FROM AUTHOR]