Antisite Defects Research Articles

NMR Spectra Particularities in LiNbO3 Crystals with a Near-Stoichiometric Composition

The paper studies LiNbO3 (LN) crystals with a near-stoichiometric composition (NSLN). The study establishes the possibility of different physical methods to reveal NSLN crystals’ exact composition. The main goal was to establish how precisely these methods can reveal a NSLN composition, including a defective structure. This structure determines properties that are important for the application of the crystals. Two NSLN crystals with a different Li/Nb ratio have been studied by IR and NMR spectroscopy. NSLN crystals have been grown from a congruent melt with different K2O flux contents (5.0 and 5.5 wt%). The data on NSLN have been compared with the data on congruent (CLN) crystals. CLN are the most widely used LN crystals. The study has established that analysis of the IR spectra can determine the Li/Nb ratio within [Li2O] = 48.6 – 50.0 mol% range, while the 93Nb NMR spectra has a wider range of sensibility. LN crystals’ stoichiometry or the Li/Nb ratio determine the concentration of antisite defects NbLi. Niobium substitutes lithium in its octahedron. Such defects appear up to [Li2O] = 49.9 mol%. Thus, the study shows that IR and NMR spectroscopy are sensitive methods that can complement each other when determining the precise LN composition (Li/Nb ratio) and the presence of intrinsic defects in the crystals.

Ce 3+:Lu 3Al 5O 12–Al 2O 3 optical nanoceramic scintillators elaborated via a low-temperature glass crystallization route

Transparent Ce:lutetium aluminum garnet (Ce:Lu₃Al₅O₁₂, Ce:LuAG) ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number (<i>Z</i>_eff). However, the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of Lu_Al antisite defects at high sintering temperatures. This work demonstrates a low-temperature (1100 ℃) synthetic strategy for elaborating transparent LuAG–Al₂O₃ nanoceramics through the crystallization of 72 mol% Al₂O₃–28 mol% Lu₂O₃ (ALu28) bulk glass. The biphasic nanostructure composed of LuAG and Al₂O₃ nanocrystals makes up the whole ceramic materials. Most of Al₂O₃ is distributed among LuAG grains, and the rest is present inside the LuAG grains. Fully dense biphasic LuAG–Al₂O₃ nanoceramics are highly transparent from the visible region to mid-infrared (MIR) region, and particularly the transmittance reaches 82% at 780 nm. Moreover, Lu_Al antisite defect-related centers are completely undetectable in X-ray excited luminescence (XEL) spectra of Ce:LuAG–Al₂O₃ nanoceramics with 0.3–1.0 at% Ce. The light yield of 0.3 at% Ce:LuAG–Al₂O₃ nanoceramics is estimated to be 20,000 ph/MeV with short 1 μs shaping time, which is far superior to that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals. These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics, and is promising to produce garnet-based ceramic materials with excellent properties, thereby meeting the demands of advanced scintillation applications.

Wide-Bandgap Perovskite Solar Cell Using a Fluoride-Assisted Surface Gradient Passivation Strategy.

Wide-bandgap (1.68 eV) perovskite solar cells (PSCs) are important components of perovskite/Si tandem devices. However, the efficiency of wide bandgap PSCs has been limited by their huge open-circuit voltage (VOC) deficit due to non-radiative recombination. Deep-level acceptor defects are identified as the major killers of VOC, and they can be effectively improved by passivation with ammonium salts. Theoretical calculation predicts that increasing the distance between F and -NH3+ of fluorinated ammonium can dramatically enhance the electropositivity of -NH3+ terminals, thus providing strong adsorption onto the negatively charged IA and IPb anti-site defects. Characterizations further confirm that surface gradient passivation employing p-FPEAI demonstrates the most efficient passivation effect. Consequently, a record-efficiency of 21.63% with the smallest VOC deficit of 441 mV is achieved for 1.68 eV-bandgap inverted PSCs. Additionally, a flexible PSC and 1 cm2 opaque device also deliver the highest PCEs of 21.02% and 19.31%, respectively.

Ag Alloying in Cu2−yAgyBa(Ge,Sn)Se4Films and Photovoltaic Devices

Trigonal Cu2BaGe1−xSnxSe4(CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu2ZnSn(S,Se)4. This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag‐incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). These results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu2ZnSn(S,Se)4, at least at the current level of absorber and device optimization.

Oxygen Anion Redox Chemistry Correlated with Spin State in Ni-Rich Layered Cathodes.

Despite the low cost and high capacity of Ni-rich layered oxides (NRLOs), their widespread implementation in electric vehicles is hindered by capacity decay and O release. These issues originate from chemo-mechanical heterogeneity, which is mainly related to oxygen anion redox (OAR). However, what to tune regarding OAR in NRLOs and how to tune it remains unknown. In this study, a close correlation between the OAR chemistry and Li/Ni antisite defects is revealed. Experiments and calculations show the opposite effects of aggregative and dispersive Li/Ni antisite defects on the NiO6 configuration and Ni spin state in NRLOs. The resulting broad or narrow spans for the energy bands caused by spin states lead to different OAR chemistries. By tuning the Li/Ni antisite defects to be dispersive rather than aggregative, the threshold voltage for triggering OAR is obviously elevated, and the generation of bulk-O2 -like species and O2 release at phase transition nodes is fundamentally restrained. The OAR is regulated from irreversible to reversible, fundamentally addressing structural degradation and heterogeneity. This study reveals the interaction of the Li/Ni antisite defect/OAR chemistry/chemo-mechanical heterogeneity and presents some insights into the design of high-performance NRLO cathodes.

Unveiling the structure-property relationship in metastable Heusler compounds by systematic disorder tuning

Heusler compounds represent a unique class of materials that exhibit a wide range of fascinating and tuneable properties such as exotic magnetic phases, superconductivity, band topology, or thermoelectricity. An exceptional, but for Heusler compounds common, feature is that they are prone to antisite defects and disorder. In this regard, the $\mathrm{Fe}{}_{2}\mathrm{VAl}$ Heusler compound has been a particularly interesting and disputed candidate. Even though various theoretical scenarios for the interplay of physical properties and disorder have been proposed, the metastable disordered A2 phase hitherto precluded experimental investigation in bulk samples. Here, we report experimental results on disorder-tuned $\mathrm{Fe}{}_{2}{\mathrm{VAl}}_{0.9}{\mathrm{Si}}_{0.1}$ alloys all the way toward the A2 phase, which we realized via rapidly quenching our samples from high temperatures. We measured the thermoelectric properties of these materials in a wide temperature range (4 to 700 K); they suggest a gradual semimetal/narrow-gap semiconductor $\ensuremath{\rightarrow}$ metal transition upon increasing the disorder. We also find a large anomalous Hall effect in the disordered A2 phase, arising from the side-jump scattering of charge carriers at the antisite magnetic moments. This is corroborated by measurements of the temperature- and field-dependent magnetization, which increases dramatically up to $\ensuremath{\approx}2.5\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\text{B}}/\mathrm{f}.\mathrm{u}.$ as compared to the ordered compound ($&lt;0.1\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\text{B}}/\mathrm{f}.\mathrm{u}.$). This study provides an experimental realization of the metastable A2 structure in bulk $\mathrm{Fe}{}_{2}\mathrm{VAl}$-based alloys and grants insight into the structure-property relationship of these materials. Our work confirms that temperature-induced antisite disorder, occurring during thermal heat treatment, can be a precisely tuneable parameter in the family of Heusler compounds.

Near-stoichiometric Er3+ doped LiNbO3 thin films prepared by vapor transport equilibration treatment

A post-growth Li-rich vapor transport equilibration (VTE) technique was used to prepare near-stoichiometric Er3+ doped LiNbO3 thin films. Er3+ fluorescence property, defect feature and Li2O content of the films were characterized. The results show that the visible and near-infrared fluorescence intensity increases remarkably by ∼10 times the VTE time is increased from 0 to 5 h. The enhancement can be explained from viewpoint of Nb4+ defects concentration. X-ray photoelectron spectrometer study confirms presence of antisite NbLi4+ in the films and NbLi4+ is major defect. Its concentration decreases with increased VTE time. The Li2O content in the films is evaluated to be 48.8–49.7 mol% from the birefringence results. It increases with a rise in VTE time, matching with the characteristic of antisite defects. As defects concentration decreases, the non-radiative transition weakens , which is beneficial to improve fluorescence properties.

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Microstructure correlated optical, electrical and mechanical characterizations of (Bi1-xSbx)2Te3: Effect of compositional variations on different properties

Nanocrystalline rhombohedral (Bi1-xSbx)2Te3 (with x = 0, 0.25, 0.5, 0.75, 1) powders are synthesized by a facile one-pot mechanical milling technique using elemental Bi, Sb, and Te powders, taken in different proportions within 3 h of milling. The Rietveld refined X-ray diffraction (XRD) patterns of the fabricated samples reveal the compositional variations of different microstructural parameters like crystallite size, lattice strain, and lattice parameters. The included impurity percentages of Bi and Sb explain the variation of lattice parameter a, whereas, the antisite defects are well interpreted with the change in lattice parameter c. The r.m.s. lattice strain is consistent with the formulation of different antisite defects acting as either n-type or p-type doping within the materials (Bi1-xSbx)2Te3. The microstructure is also revealed from the field-emission scanning electron microscope (FESEM) image and energy dispersive X-ray (EDX) spectrum and compared with the results obtained from the XRD pattern analysis. The narrow bandgaps of the materials are determined from the Fourier transform infrared (FTIR) spectra, and the correlation with the microstructure establishes their changes with the compositional x value. Here, both the blue and red shifts in bandgap with particle size variations are observed and explained. The positions of the conduction and valence bands are determined with composition variations (x). The non-Debye type, thermally activated conduction process of the semiconducting materials is confirmed from the ac electrical study of the samples at room and high temperatures. The variation of electrical conductivity with different alloying concentrations and temperatures is explained in terms of their particle size and density of antisite defects. The conduction mechanism is found to be a small polaron hopping model. The Vickers microhardnesses of the samples are measured and explained by correlating with the microstructural parameters. The Meyer's law establishes the normal indentation size effect (ISE). The microhardness of the materials partially supports the conductivity results.

Unraveling thermally induced spin reorientation of composite component NdFe0.5Cr0.5O3 system

Sophisticated spin instruments require high-precision spin control. In this study, we accurately study the intrinsic magnetic properties of the strongly disordered system NdFe0.5Cr0.5O3 through molecular field models combined with anti-site defects (ASD) theory. The three constituent sub-magnetic phases of the system are separated, and their magnetization contributions are calculated separately. Fitting the angle of the A/B magnetic moment at a given temperature, the reorientation temperature point and temperature dependence of different magnetic phases are obtained. This research will provide a very good theoretical support for studying complex disordered systems and applying high-precision spin control and lay a foundation for the design of new functional materials.

Oriented adsorption and efficient sensing of NO2 on MoSe2 monolayer: a comparative study with WSe2 monolayer

Oriented adsorption is very rare on two-dimensional inorganic thin layers. Based on preliminary study, density functional theory (DFT) was used to explore the adsorption and sensing behavior of NO2 on MoSe2 perfect and defective monolayers including selenium vacancy (VSe), molybdenum vacancy (VMo), and antisite defect of selenium on molybdenum site (SeMo) by large-scale sampling. The adsorption energy can reach 0.29 eV with 0.182 e charge transfer on the perfect monolayer. The adsorption ability is improved largely on VSe, VMo, and SeMo monolayers (3.27, 0.93, and 1.20 eV) with considerable charge transfer (0.583, 0.152, and 0.139 e, respectively), demonstrating the potential of MoSe2 monolayers as NO2 sensing materials. Meanwhile, similar to WSe2 monolayer, oriented adsorption of NO2 is disclosed. NO2 molecule extends mainly along the Se–Mo–Se trough and the Se–Mo bond on all the four MoSe2 monolayers. Whereas, the oriented adsorption ability is weaker than the WSe2 monolayer, which can be confirmed by the relatively small proportion of oriented adsorption conformations. This kind of double oriented adsorption behavior (vertical adsorption and adsorption along specific direction of the two-dimensional material) was considered to be due to the good polarity match between molecule and monolayer. Molecular dipole moment and material bond population are believed to be two important parameters that determine the oriented adsorption capacity of molecular-material systems. The successive discovery of the unique oriented adsorption and the deepening of understanding provide chance for molecular design of oriented adsorption of inorganic small molecules on two-dimensional layered materials. The strong dissociation ability of the anionic vacancy monolayer to NO2 molecule indicates that MoSe2 monolayer has a very high adsorption, capture, and activation potential for nitrogen oxides. Comparative study proved that the Mo site activity was less than the W site activity on the perfect monolayer, and defects could help the Mo site activity overtake. These findings provide pivotal guidance for creating advanced surface regulated electronic systems, such as sensors.

Growing, Structure and Optical Properties of LiNbO3:B Crystals, a Material for Laser Radiation Transformation

Physical and chemical properties have been studied in lithium niobate (LiNbO3, LN) crystals grown by Czochralski from a boron doped melt. Optical uniformity and optical damage resistance of LiNbO3:B crystals have been compared with control crystals of nominally pure congruent (CLN) and near-stoichiometric (NSLN K2O) composition. LiNbO3:B crystals structure has been studied. Studied LiNbO3:B crystals have been grown from differently synthesized charges. The charges have been synthesized from a mixture Nb2O5:B-Li2CO3 using homogeneously doped Nb2O5:B precursor (sample 1, (B) = 0.0034 wt% in the charge) and by a direct solid phase synthesis from Nb2O5-Li2CO3-H3BO3 mixture (sample 2, (B) = 0.0079 wt% in the charge). Only traces of boron (10-5-10-4 wt%) have been detected in the samples. We have established that concentration of anti-site defects NbLi is lower in both LiNbO3:B than in CLN crystals. XRD analysis has confirmed that B3+ cations localize in faces of tetrahedral voids O4 of LN structure. The voids act as buffers at the anion sublattice distortion. Sample 1 has been shown to have a structure closer to NSLN K2O crystal than sample 2. We have also shown that the chemical purity of LN crystal increases compared to the melt purity because boron creates strong compounds with impurities in the melt system Li2O-Nb2O5-B2O3. Metals impurities thus stay in the melt and do not transfer to the crystal.

Intrinsic Defects and the Inducing Conduction Mechanism of Langasite-Type High-Temperature Piezoelectric Crystals.

Increasing the crystal resistivity is critically important for enhancing the signal-to-noise ratio and improving the sensing capability of high-temperature piezoelectric sensors based on langasite-type crystals. The resistivity of structural ordered langasite-type crystals is much higher compared to that of the disordered crystals. Here, we selected structural ordered Ca3TaGa3Si2O14 (CTGS) and disordered La3Ga5SiO14 (LGS) as representatives to investigate the microscopic conduction mechanism and further reveal the origin of the different resistivities of the ordered and disordered langasite-type crystals at elevated temperatures. By combining first-principles calculations and experimental investigations, we found that the different conductivity behaviors of the ordered and disordered crystals originate from different types of point defects formed in the crystal and their different contributions to the conductivity. For the disordered LGS crystal, the oxygen vacancies are apt to be formed at high temperatures, promoting the transition of valence electrons and yielding high conductivity. For the ordered CTGS crystal, the dominant TaGa antisite defects can introduce an electron-hole recombination center in the electronic band gap, significantly shortening the carrier lifetime and thus reducing the conductivity. This provides effective guidance to improve the resistivity performance of langasite-type crystals at high temperatures by optimizing the experimental conditions, such as oxygen atmosphere treatment, antisite defect modification, etc.

Tuning the magnetic ordering driven by cationic antisite defects in the Li(ZnMn)As system.

The electronic structure and magnetic properties of Li(ZnMn)As with antisite defects have been investigated by using first-principles calculations within the Perdew-Burke-Ernzerhof generalized gradient approximation. The cation antisite defect induced by Zn substitution for As was considered. Mn-3d, As-4p, Zn-4s, and Zn-4p were involved in the formation of d-sp hybrid orbitals, which enhanced the non-localized properties of Mn-3d electrons and provided a channel of Mn(↑)-As(↓)-ZnAs(↓)-Mn(↑) for indirect exchange of electrons between the magnetic ions. The antisite defect of Zn-substituted As belonged to the acceptor doping, rendering the compound p-type characteristics. The existence of the extra free hole carriers regulated the magnetic ordering transition. The ferromagnetic coupling between the Mn magnetic dopants was more favorable in the system with an antisite defect. In this paper, a novel type of dilute magnetic semiconductor with controllable carriers was designed and the mechanism of ferromagnetic coupling was revealed, which provided a theoretical reference for the subsequent studies.

Triggering reversible anion redox chemistry in O3-type cathodes by tuning Na/Mn anti-site defects

We propose the triggering of reversible anion redox chemistry in the O3-NaMn1/3Fe1/3Ni1/3O2 cathode by tuning Na/Mn anti-site defects with Ho doping.

Stoichiometry matters: correlation between antisite defects, microstructure and magnetic behavior in the cathode material Li1−zNi1+zO2

Using synchrotron X-ray and neutron diffraction, NMR and magnetometry techniques, this study reveals how point defects evolve and critically affect particle growth and magnetic properties in the cathode material Li1−zNi1+zO2 (−0.05 ≤ z ≤ 0.35).

Comparative studies of interatomic potentials for modeling point defects in wurtzite GaN

In this paper, a new version of the Stillinger–Weber (SW) potential for wurtzite GaN is presented, by which we systematically explore the structural and thermodynamical properties of native point defects and their complexes. In parallel, the semi-empirical Modified Embedded-Atom Method (MEAM) potential is selected for comparison. The SW and MEAM potentials are assessed by the reproduction of the fundamental properties of wurtzite GaN and by the ability to describe the inversion domain boundaries and the wurtzite–rocksalt phase transition. Then the structural search of native point defects and their complexes in GaN is implemented using both SW and MEAM potentials with the benchmark of Density Functional Theory (DFT) calculations. Besides vacancies and antisites, four N and five Ga interstitials are confirmed by refining the DFT calculations, among which two N split interstitials N+−N⟨21̄1̄0⟩ and N+−Ga⟨011̄0⟩, and two Ga split interstitials, Ga+−Ga⟨011̄0⟩−g and Ga+−N⟨011̄0⟩, are observed for the first time. The SW potential correctly predicts the octahedral occupation GaOct to be the most stable Ga interstitial, while the MEAM potential predicts the ground state of the N+−N⟨011̄0⟩ split interstitial (N+−N⟨011̄0⟩−g) as the most stable N interstitial. However, neither of the two potentials could simultaneously generate the most stable configurations of N and Ga interstitials. The investigations of point defect complexes reveal that N octahedral Frenkel [FrenkelOct(N)] and paired antisite (NGaGaN) defects are unstable and get converted into VN⊕N+−N⟨011̄0⟩−g configurations with different separations between VN and N+−N⟨011̄0⟩−g point defects based on the DFT calculations. The formation energies calculated by the DFT and SW potential demonstrate that Schottky, Ga octahedral Frenkel [FrenkelOct(Ga)], and VN⊕N+−N⟨011̄0⟩−g point defect complexes are energetically feasible and that they should not dissociate into two isolated point defects. In contrast, the MEAM potential predicts the dissociation to be exothermic for Schottky and VN⊕N+−N⟨011̄0⟩−g. Overall, the structural features concerned with N–N or Ga–Ga bonds relaxed by the SW potential are more consistent with DFT calculations than the MEAM counterpart.

Широкополосная ЭПР-спектроскопия кристалла Lu-=SUB=-3-=/SUB=-Al-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-:Tb-=SUP=-3+-=/SUP=-

In a single crystal of lutetium aluminum garnet (Lu3Al5O12, LuAG) in the frequency range of 37–210 GHz, at a temperature of 4.2 K, the EPR spectra of non-Kramers Tb3+ impurity ions were recorded. The measurement results indicate that Tb3+ ions replace Y3+ ions in the dodecahedral position with local D2 symmetry. The value of the g factor, the hyperfine structure constant, and the energy interval between the ground and the first excited nondegenerate sublevels of the ground multiplet are determined. Weak satellite signals were also registered, the origin of which is associated with the formation of antisite defects in the environment of paramagnetic Tb3+ centers.

Cu2ZnSnS4 monograin layer solar cells for flexible photovoltaic applications.

Monograin powder technology is one possible path to developing sustainable, lightweight, flexible, and semi-transparent solar cells, which might be ideal for integration with various building and product elements. In recent years, the main research focus of monograin technology has centered around understanding the synthesis and optoelectronic properties of kesterite-type absorber materials. Among these, Cu2ZnSnS4 (CZTS) stands out as a promising solar cell absorber due to its favorable optical and electrical characteristics. CZTS is particularly appealing as its constituent elements are abundant and non-toxic, and it currently holds the record for highest power conversion efficiency (PCE) among emerging inorganic thin-film PV candidates. Despite its advantages, kesterite solar cells' PCE still falls significantly behind the theoretical maximum efficiency due to the large VOC deficit. This review explores various strategies aimed at improving VOC losses to enhance the overall performance of CZTS monograin layer solar cells. It was found that low-temperature post-annealing of CZTS powders reduced Cu-Zn disordering, increasing Eg by ∼100 meV and VOC values; however, achieving the optimal balance between ordered and disordered regions in kesterite materials is crucial for enhancing photovoltaic device performance due to the coexistence of ordered and disordered phases. CZTS alloying with Ag and Cd suppressed non-radiative recombination and increased short-circuit current density. Optimizing Ag content at 1% reduced CuZn antisite defects, but higher Ag levels compensated for acceptor defects, leading to reduced carrier density and decreased solar cell performance. Co-doping with Li and K resulted in an increased bandgap (1.57 eV) and improved VOC, but further optimization is required due to a relatively large difference between measured and theoretical VOC. Heterojunction modifications led to the most effective PCE improvement in CZTS-based solar cells, achieving an overall efficiency of 12.06%.

Wide-band EPR spectroscopy of a Lu-=SUB=-3-=/SUB=-Al-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-:Tb-=SUP=-3+-=/SUP=- crystal

In a single crystal of lutetium aluminum garnet (Lu3Al5O12, LuAG) in the frequency range of 37-210 GHz, at a temperature of 4.2 K, the EPR spectra of non-Kramers Tb3+ impurity ions were recorded. The measurement results indicate that Tb3+ ions replace Y3+ ions in the dodecahedral position with local D2 symmetry. The value of the g factor, the hyperfine structure constant, and the energy interval between the ground and the first excited nondegenerate sublevels of the ground multiplet are determined. Weak satellite signals were also registered, the origin of which is associated with the formation of antisite defects in the environment of paramagnetic Tb3+ centers. Keywords: hyperfine interaction, rare earth ions, spin Hamiltonian, non-Kramers ion.