Rb Site Research Articles

Effect of metal (Cr, Sr, Ag, Cu) doping on the performance of lead-free RbSnI3 based perovskite solar cells: A theoretical approach

Perovskite solar cells based on lead have witnessed unprecedented growth over the past decade, achieving an impressive power conversion efficiency (PCE) of 26.1%. However, lead toxicity remains a concern for commercialization. In order to resolve the matter, scientists have been investigating alternative materials; in this context, rubidium-based lead-free perovskites like RbSnI3 may be a promising alternative because it has a high optical conductivity and absorption coefficient. Density Functional Theory (DFT)-based first-principles studies are used in this work to examine the effect of metal doping (specifically Cr, Sr, Ag, and Cu) on the optoelectronic and structural characteristics of orthorhombic RbSnI3 perovskite. In addition, we conducted a comprehensive study to investigate the impact of metal doping on the formation energy, structural stability, and HOMO–LUMO energy levels of RbSnI3 perovskite. Introducing transition metal cations (Cr2+, Ag+, and Cu+) at the Rb site results in a flat band in the conduction band region, transforming the RbSnI3’s indirect band gap into a direct one and significantly affecting the optoelectronic properties. The DFT results are then integrated into the Solar Cell Capacitance Simulator (SCAPS-1D) to estimate the effectiveness of the modeled device. The Cu-doped RbSnI3 device exhibits the highest PCE of 20.2%. Furthermore, Ag and Cu doping in RbSnI3 increases bond length, which reduces exciton binding energy and helps with charge carrier generation.

Structures of dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), from laboratory X-ray powder diffraction data and DFT calculations.

The crystal structures of the isostructural compounds dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The compounds are isostructural to K3C6H5O7(H2O) and Rb3C6H5O7(H2O), but exhibit different degrees of ordering of the K and Rb cations over the three metal-ion sites. The K and Rb site occupancies correlate well to both the bond-valence sums and the DFT energies of ordered cation systems. The MO6 and MO7 coordination polyhedra share edges to form a three-dimensional framework. The water mol-ecule acts as a donor in two strong charge-assisted O-H⋯O hydrogen bonds to carboxyl-ate groups. The hydroxyl group of the citrate anion forms an intra-molecular hydrogen bond to one of the central carboxyl-ate oxygen atoms.

ChemInform Abstract: Variable-Temperature 87Rb Magic-Angle Spinning NMR Spectroscopy of Inorganic Rubidium Salts

Temperature dependencies of the 87Rb quadrupole coupling constants (CQ), asymmetry parameters (ηQ), and isotropic chemical shifts (δiso) have been observed and determined for RbCl, RbClO4, Rb2SO4, and RbNO3 from variable-temperature (VT) 87Rb magic-angle spinning (MAS) NMR spectra for the temperature range from about −100 to +165 °C. VT 87Rb multiple-quantum MAS NMR spectra of the trigonal form for RbNO3 have assisted the retrival of CQ, ηQ, and δiso for the three Rb sites of this phase. The results demonstrate that CQ(87Rb) and δiso(87Rb) are highly temperature-dependent for all samples over the studied temperature range. Linear correlations of δiso with temperature, corresponding to temperature coefficients in the range −0.014 to −0.036 ppm/°C (i.e., increasing shielding with increasing temperature), are observed for all samples. An exception is the Rb(2) site in Rb2SO4 for which a small linear decrease in shielding is observed with increasing temperature. For RbClO4 and Rb2SO4 the three CQ(87Rb) values...

R 87 b and C133s nuclear magnetic resonance study of the structural properties of mixed RbxCs2−xZnCl4 (x=, 1, and 2) crystals

The structures of mixed RbxCs2−xZnCl4 (x=0, 1, and 2) single crystals grown by using the slow evaporation method were determined with x-ray diffraction. In addition, the NMR spectra and the spin-lattice relaxation times, T1, of the R87b and C133s nuclei of the three crystals were determined by using nuclear magnetic resonance (NMR) spectroscopy. The spin-lattice relaxation times, T1, of the Cs-based compounds are very much longer than those of the Rb-based compounds. The differences between the T1 values of the Rb and Cs nuclei are due to the difference between their electric quadrupole moments. Further, we analyzed the crystallographic structures of these crystals by considering the occupation probabilities (Rb or Cs) of the two cationic sites. Our NMR experimental results confirm that there are two crystallographically inequivalent Rb sites, Rb(1) and Rb(2), in Rb2ZnCl4 and two crystallographically inequivalent Cs sites, Cs(1) and Cs(2), in Cs2ZnCl4. And, only one Rb site and only one Cs site in RbCsZnCl4 was obtained. The Cs and Rb occupation rates of each of the two available sites, A1 and A2, were determined from the NMR signals.

A study of the phase transitions and ionic motions of RbH 3(SO 4) 2 single crystals by 1H and 87Rb NMR

The 1H and 87Rb spin–lattice relaxation and spin–spin relaxation times of RbH 3(SO 4) 2 single crystals grown using the slow evaporation method were measured using FT NMR spectrometry near the newly identified phase transition temperatures: the successive phase transition temperatures 342 K (= T C3), 408 K (= T C2), and 490 K (= T C1) were determined by carrying out differential scanning calorimetry (DSC) measurements. The spin–lattice relaxation time, T 1, of 1H in RbH 3(SO 4) 2 crystals below T C3 exhibits a minimum, indicating the presence of molecular motion governed by the Bloembergen–Purcell–Pound (BPP) theory. The observation of liquid-like values of the spin–spin relaxation time, T 2, is consistent with superionic characteristics. Although the results for 1H relaxation provide no evidence of the phase transition at T C3, the 87Rb relaxation time changes abruptly at T C2 and T C3, indicating that the T 1 of the 1H and 87Rb nuclei depend on their local environments. Further, we found that the change in the splitting of the Rb resonance line at T C3 is associated with a change in the local symmetry at the Rb site. In conclusion, the newly identified phase transitions of RbH 3(SO 4) 2 crystals are accompanied by slight rotations of the sulphate group and by slight distortions of the lattice in the neighborhood of the Rb + ions. These results are compared with those obtained for Rb 3H(SO 4) 2 crystals, which have similar hydrogen-bonded structures.

Solid-State 87Rb NMR Study in Powdered RbMnCl3

Structural phase transition at 290 K and the implication on the intermediate phase above 290 K in powdered RbMnCl3 are observed by using a solid-state 87Rb NMR spectroscopy. Quadrupole coupling constants (e2qQ/h), the asymmetry parameters (η), and the relative peak intensities for two physically nonequivalent Rb sites, Rb(I) and Rb(II), are determined from nonlinear least-squares fits to the 87Rb NMR powder patterns in the temperature range from 260 to 330 K. Quadrupole coupling constants and the asymmetry parameters are examined for the detection of the phase transition resulting in a significant structural change in the Rb(II) site. In addition, changes in the relative peak intensity between the Rb(I) and Rb(II) sites seem to suggest the existence of an anomalous intermediate phase, which is complemented by the differential scanning calorimetry and X-ray diffraction studies.

Variable-Temperature 87Rb Magic-Angle Spinning NMR Spectroscopy of Inorganic Rubidium Salts

Temperature dependencies of the 87Rb quadrupole coupling constants (CQ), asymmetry parameters (ηQ), and isotropic chemical shifts (δiso) have been observed and determined for RbCl, RbClO4, Rb2SO4, and RbNO3 from variable-temperature (VT) 87Rb magic-angle spinning (MAS) NMR spectra for the temperature range from about −100 to +165 °C. VT 87Rb multiple-quantum MAS NMR spectra of the trigonal form for RbNO3 have assisted the retrival of CQ, ηQ, and δiso for the three Rb sites of this phase. The results demonstrate that CQ(87Rb) and δiso(87Rb) are highly temperature-dependent for all samples over the studied temperature range. Linear correlations of δiso with temperature, corresponding to temperature coefficients in the range −0.014 to −0.036 ppm/°C (i.e., increasing shielding with increasing temperature), are observed for all samples. An exception is the Rb(2) site in Rb2SO4 for which a small linear decrease in shielding is observed with increasing temperature. For RbClO4 and Rb2SO4 the three CQ(87Rb) values...

Localization and Charge Conversion of Copper in Rb2ZnCl4:Cu Crystals: An ESR and Optical Absorption Study

Electron spin resonance and optical studies reveal the presence of both Cu 2+ and Cu + centers in Rb 2 ZnCl 4 :Cu single crystals grown from melt and their conversion by X- or γ-irradiation. Two types of paramagnetic Cu 2+ centers with different concentrations and production properties have been identified. The more abundant Cu 2+ (I) center consists of a Cu 2+ (II) center seems to be situated at a Rb site. Production experiments strongly suggest that during the crystal growth copper enters the Rb 2 ZnCl 4 lattice as Cu 2+ , mainly at Zn 2+ sites, part of it being afterwards converted to Cu + precursor centers. The presence of a neighboring charge compensating anion vacancy and its departure during the radiolytic Cu + (I)→Cu 2+ (I) conversion seems to play an essential role in the stabilization of the Cu + (I) and Cu 2+ (I) centers, respectively.

87Rb NMR of the structural phase transition in RbSCN.

The second-order shifts of the $^{87}\mathrm{Rb}$ 1/2\ensuremath{\rightarrow}-1/2 NMR transitions have been measured in RbSCN above and below ${\mathit{T}}_{\mathit{c}}$=435 K for crystal rotations around the a, b, and c axes. Whereas below ${\mathit{T}}_{\mathit{c}}$ the $^{87}\mathrm{Rb}$ electric-field gradient (EFG) and chemical shift tensors are compatible with the Rb site symmetry as given by the orthorhombic space group ${\mathit{D}}_{2\mathit{h}}^{11}$(Pbcm), this is not the case for the EFG data above ${\mathit{T}}_{\mathit{c}}$. The results show that the symmetry of the high-temperature tetragonal phase is dynamically broken on the Larmor frequency (${10}^{\mathrm{\ensuremath{-}}8}$ s) time scale whereas symmetry-breaking terms are averaged out on the ``site'' splitting, domain splitting, and chemical shift tensor (\ensuremath{\simeq}${10}^{\mathrm{\ensuremath{-}}2}$--${10}^{\mathrm{\ensuremath{-}}3}$ s) time scales. $^{87}\mathrm{Rb}$ NMR thus allows for an observation of the phase transition in RbSCN in the ``slow motion'' regime where the high-temperature phase is seen to consist of a large number of orthorhombic microdomains with lifetimes longer than ${10}^{\mathrm{\ensuremath{-}}7}$ s and shorter than ${10}^{\mathrm{\ensuremath{-}}3}$ s.

Rb NMR study of the electronic properties of Rb 1C 60

87Rb (and 85Rb) NMR spectra in the orthorhombic phase ( (o) phase) of Rb 1C 60 show up broadening, with respect to the high-T cubic phase and to the quenched phase, which signals change of symmetry of the Rb site. The spin lattice relaxation rate follows a linear T dependence in the (o) phase above 100 K, suggesting that this phase is metallic. The increase of 1/T 1T at low T seems to be correlated with the transition seen by E.S.R.

Confirmation of Rb gene defects in B-CLL clones and evidence for variable predominance of the Rb defective cells within the CLL clone.

In 70 B-CLL patients, deletion or translocation, at or near the retinoblastoma (Rb) site, was detected in 20 by cytogenetic analysis. Purified B cell clones from 13 of these B-CLL patients were isolated and studied for Rb gene status, Rb mRNA and the Rb protein product. Southern blot analysis of the Rb site detected internal deletions (N = 1) or a single allele loss (N = 2) in five patients. Northern blots detected reduced Rb mRNA in four patients. Immunoblot of whole cell lysate revealed reduced levels of unphosphorylated Rb protein in six CLL patients. No CLL B cell clone contained phosphorylated Rb species. These molecular studies have confirmed the cytogenetic alteration of 13q12-14 sites in B-CLL cells. In addition, cytogenetic and molecular biologic analysis suggest heterogeneity in the B cell clone for Rb gene abnormality. B-CLL patients with abnormalities in both cytogenetic and Rb DNA/RNA analysis will have a dominance of B cells with an Rb abnormality (N = 5). In patients whose Rb defective CLL cells constitute only a minor subpopulation of the total B cell clone, only cytogenetic defects would likely be detected (N = 7).

87,85Rb NMR spectra and relaxation in Rb 3C 60

85,87Rb NMR spectra and relaxation are reported in the temperature range 4–300 K, for samples of C 60 intercalated with Rb through a direct-reaction technique at the nominal composition Rb 3C 60. The NMR spectrum is characteristic of the second-order quadrupole powder distribution of the central line, indicating a local non-cubic symmetry at the Rb site and a very small Knight shift. The relaxation rate is found to follow a T 2 law above 30 K. This result, together with the ratio of the relaxation for the two Rb isotopes, points towards a quadrupole relaxation mechanism by phonons. Two contributions were found in the nuclear magnetization recovery which have been attributed to the Rb nuclei in the tetrahedral site and in the octahedral site, respectively, with the nucleus in the T-site coupled more strongly to the lattice dynamics. No detectable change in the NMR spectrum and/or relaxation rates was found at the superconducting transition located at T c = 27.5 K.

Determination of the electric field gradient in RbCaF3 near the phase transition

Abstract The fluoroperovskite, RbCaF 3 undergoes a phase transition at 195.5K from a cubic to a tetragonal phase. The order parameter for this transition is directly related to the electric field gradient which arises in the tetragonal phase. In this work, we have used three NMR methods to measure the electric field gradient at the 87 Rb site in a single crystal of RbCaF 3 , very near this transition. These experiments are based on recent theoretical developments which allow the measurement of quadrupole parameters even for nuclei in a weak electric field gradient.

Self-trapping of free excitons in mixed K1− xRbxI crystals

Thermal quenching of free-exciton luminescence in mixed K 1− x Rb x I crystals has been investigated in order to clarify the processes of exciton self-trapping in mixed random systems. The self-trapping rate of free excitons has been calculated in the semiclassical approximation, in satisfactory agreement with the experimental data. The analysis shows that free excitons in mixed K 1− x Rb x I> crystals are preferentially self-trapped in the vicinity of an Rb site. The self-trapping rate increases in the middle concentration regions, compared with those in the pure substances, due to cooperative enhancement of random potentials and lattice distortions.

NMR study of 87Rb nuclei in RbCaF 3 at high pressures and low temperatures near the structural phase transition

An apparatus was designed and built for pulsed NMR measurements at pressures as high as 7 kbar and low temperatures in the range of 100 to 300 K, with 2 mK stability. The first experimental results obtained are on 87Rb nuclei in RbCaF 3 perovskite, which undergoes a structural first order phase transition from cubic to tetragonal symmetry. Spin-lattice relaxation time measurements were performed for three different isobars from the transition temperature up into the cubic phase. The pressure derivative of the transition temperature for this material is 2.7 K kbar −1, and will be compared with other perovskites. From the Clausius-Clapeyron equation we derive the latent heat of the transition, which has the same order of magnitude as the data from thermal measurements. In the cubic phase, far from T c, the activation energy of the motion modulating the electric field gradient (efg) at the Rb site is obtained at 1 bar, 3350 bar and 5400 bar.

Rb87nuclear-magnetic-resonance study of the cubic to tetragonal phase transition in RbCaF3

The static and dynamical phenomena occurring around the structural phase transition at ${T}_{c}\ensuremath{\simeq}195.90\ifmmode\pm\else\textpm\fi{}0.15$ K in RbCa${\mathrm{F}}_{3}$ have been investigated by means of $^{87}\mathrm{Rb}$ Fourier-transform NMR measurements. The second-order shift of the central line due to the static quadrupole perturbation has been related to the electric field gradient arising at the Rb site below ${T}_{c}$ and the temperature dependence of the angle of rotation $\ensuremath{\varphi}$ of the Ca${\mathrm{F}}_{6}$ octahedra has been obtained. The $^{87}\mathrm{Rb}$ spin-lattice relaxation rate above ${T}_{c}$ has been related to the rotational fluctuations of the octahedra induced by the critical-soft-mode branches, from which information on the symmetry and the anisotropy of the fluctuations are derived. The analysis of the results shows: (i) below $T\ensuremath{\simeq}170$ K the temperature dependence of $\ensuremath{\varphi}$ is well described by the classical mean-field approximation, with critical exponent $\ensuremath{\beta}=\frac{1}{2}$ and extrapolated transition temperature ${T}_{0}=220$ K; (ii) above about 170 K a nonclassical critical behavior is evidenced, the apparent critical exponent being not equal to $\frac{1}{3}$, suggesting a possible changeover in the dimensionality of the correlations of the rotations; (iii) the rotational fluctuations appear to be predominantly of ${R}_{25}$ symmetry but strongly anisotropic, i.e., only slightly correlated in adjacent (100) planes as is consistent with the hypothesis of softening of a large portion of the $R\ensuremath{-}M$ branch. Order-of-magnitude estimates for the static angle of rotation as well as for the degree of anisotropy of the fluctuations are also obtained and discussed.

87Rb NMR in Ferroelectric RbH3(SeO3)2

The temperature dependence of electric field gradient (EFG) at Rb site in RbH 3 (SeO 3 ) 2 is studied by the second order quadrupole shift. The number of inequivalent Rb sites in the paraelectric and the ferroelectric phases agrees with that deduced from the consideration based on the crystal symmetry. It is found that the change in EFG caused by the phase transition behaved as the order parameter did. The existence of the intermediate incommensurate phase could not be confirmed.

Evidence for a first-order phase transition at 209 K in the superionic conductor RbAg4I5

By nuclear quadrupole resonance we have found evidence that the structural phase transition at 209 K in RbAg 4 I 5 is of first rather than of second order. In addition, the point group symmetry of the Rb site in the α-phase is lower than 3. Finally, a preliminary value of 25 MHz for the inverse correlation time of the Ag ion diffusion is obtained at 150 K.