Immobile Vacancies Research Articles

Rare earth tantalate coating materials for thermal and oxidation protection of carbon-carbon composites

To protect carbon/carbon composites against thermal corrosion and high-temperature oxidation, the thermal/oxygen barrier properties and static oxidation behavior of rare earth tantalates (YbTaO4 and LuTaO4) are investigated here. Both samples with the m' phase are successfully fabricated. The formation of oxygen vacancies benefits from atomic substitution and valence variation and the widths of the domain boundaries (18–23 nm) are close to the phonon mean free path. Low thermal conductivity is caused by Umklapp phonon-phonon scattering, oxygen vacancies and domain walls, with LuTaO4 having a value of 1.903 W m−1 K−1 at 900 °C. Furthermore, LuTaO4 has decreased oxygen-ion conductivity due to a high activation energy and immobile vacancies. A LuTaO4/Si coating can efficiently prevent the oxidation of C/C composites at 1100 °C for 15 h. The coating failure results from oxygen penetrating along the microscopic cracks and mismatch of the thermal expansion coefficients.

Early-stage structure and evolution mechanism of hydrogen supersaturated surface layers on tungsten under low-energy plasma exposure

Trapping at irradiation-induced defects significantly enhances hydrogen-isotope retention in metals with low hydrogen solubility. Here, we present the first microscopic observation of nanocavity formation on tungsten surfaces exposed to low-dose hydrogen plasma at room temperature. The nanocavities exhibit very high aspect ratios between their lateral size L and thickness ω (L/ω: 60-90) and represent the predominant microstructural defects in the early development stage of the hydrogen supersaturated surface layer on hydrogen plasma-irradiated tungsten (see Nucl Fusion57 (2017) 016026, Acta Mater201 (2020) 55). We also quantify the vacancy yield in tungsten under hydrogen irradiation with ion energies below the threshold to create stable Frenkel pairs. Such defect production at sub-threshold energy is conventionally deemed impossible, but we consider that the exposed surface acts as a defect sink with strong absorption bias for mobile self-interstitial atoms from temporarily created Frenkel pairs. This results in a high excess of immobile vacancies in the nanometer-thin surface layer and their agglomeration causes the evolution of large, disc-like nanocavities.

Mechanism of remote vacancy emergence by a supersonic crowdion cluster in a 2D Morse lattice

The supersonic M×N-crowdions are excited in a two-dimensional lattice by giving sufficiently large initial velocity v to the M×N block of atoms along a close-packed direction, where N is the number of neighboring atoms in one close-packed row and M is the number of neighboring rows. In this study, dynamics of a pair of quasi-1D supersonic 1×2-crowdions moving in parallel close- packed atomic rows separated by one non-excited atomic row (middle row) are investigated in 2D triangular Morse lattice by means of molecular dynamics simulations. It is shown that when a certain threshold excitation energy value is exceeded, the motion of these two 1×2-crowdions leads to creation of a remote vacancy in the middle row at a significantly long distance from the initiation point at the moment, when the supersonic stage of the crowdion propagation turns into subsonic one. This distance is directly proportional to the excitation energy of the 1×2-crowdion pair. The mechanism of vacancy formation is related to appearance of a Frenkel pair in the middle row, namely an immobile vacancy and an interstitial atom, which, together with the two interstitials in the outermost rows, forms the stable subsonic 3×1-crowdion cluster. It is concluded that the crowdion propagation can be accompanied by not only mass transfer but also plays a role in the formation of atomic vacancies inside crystal lattices.

Deep Proton Insertion Assisted by Oxygen Vacancies for Long‐Term Memory in VO2 Synaptic Transistor

AbstractReversible phase transformation of correlated oxides by field‐driven ionic process present opportunity to efficiently transduce between ionic transfer and electrical currents in insertion‐based reconfigurable transistors. However, the switching rate of insertion transistors is fundamentally limited by the slow rate of ionic insertion into the lattices of correlated oxides. Here, it is demonstrated that preformed oxygen vacancies in VO2−δ lattices strongly accelerate proton insertion by low gate voltage in synaptic transistors. As the degree of oxygen deficiency δ increases in VO2−δ transistors, the steepness of phase transformation and transconductance increase during the voltage sweep at the expense of the channel current modulation. Theoretical and experimental analyses reveal that the accelerated of H+ kinetics in the VO2−δ lattice occurs because immobile oxygen vacancies reduce the energy barrier to H+ migration. In an electronic synapse, this facile H+ migration in VO2−δ lattices renders “inscribed” memory by positioning the H+ neurotransmitter far from the electrolyte/VO2−δ interface. This discovery suggests a strategy to improve the learning and memory processes of artificial synaptic devices by controlling the density of intrinsic defects in the lattice framework to achieve efficient ion exchange.

Electrical properties of calcia-stabilised zirconia ceramics

The electrical properties of cubic, calcia-stabilised zirconia ceramics, CaxZr1-xO2-x: 0.12 ≤ x ≤ 0.18 have been investigated using impedance spectroscopy to separate bulk, grain boundary and electrode contact impedances. The most appropriate equivalent circuit to characterise the bulk response required inclusion of a dielectric component, represented by a series RC element, in parallel with the oxide ion conductivity represented by a parallel combination of a resistance, capacitance and constant phase element. The dielectric component may be attributed to defect complexes involving immobile oxygen vacancy pairs whereas long range conduction involves single oxygen vacancies.

The interaction between vacancies and twin walls, junctions, and kinks, and their mechanical properties in ferroelastic materials

Vacancies strongly interact with twin boundaries and often change dramatically the properties of the ferroelastic material. However, the understanding of this behavior at an atomic-level is still deficient. Here we study vacancy diffusion processes across very large length- and time-scales using a combination of molecular dynamics and Monte Carlo simulations. We find that vacancies reduce their energy by residing at twin boundaries, kinks inside domain boundaries, and junctions between domain boundaries. Vacancies have the largest binding energy inside junctions and co-migrate with the motion of the junctions. For the weaker trapping inside twin boundaries, a “ghost line” may be generated because vacancies do not necessarily diffuse with moving boundaries and are left behind, leaving a trace of a previous position of the domain boundary. Needle twins act as channels for fast diffusion with almost one order of magnitude higher vacancy diffusivity than in bulk. The relative concentration of vacancies at twin boundaries (ρVa) is a function of the average vacancy concentration (CVa) with ρVa ∼ CVaα and α = 0.61, in contrast to that of immobile vacancies case with α = 0.4. The concentration of vacancies at twin boundaries is enriched ca. 5 times at low temperatures. With increasing temperature, the enrichment drops as the trapping potential at the twin boundaries decreases (thermal release). The distribution of energy-drop upon twin pattern evolution follows a power law. The exponent ε increases from ∼1.44 to 2.0 when the vacancy concentration increases. The power law exponent is the same in the athermal region, while Vogel-Fulcher behavior is found at high temperatures.

Accumulation of Defects in Austenitic Stainless Steels with Phosphorus and Titanium Additions upon Electron Irradiation at 573 К Investigated Using Positron Annihilation Spectroscopy

Using the positron annihilation spectroscopy method, the accumulation of vacancy-type defects in steels Kh16N15М3 and Kh16N15М3T1 alloyed with phosphorus has been studied at early stages of irradiation at a temperature of 573 К. The obtained data have showed that vacancies in the steels interact with phosphorus atoms at this temperature with the formation of immobile and low-mobile vacancy—impurity complexes, which results in the accumulation of vacancy-type defects. In the steel Kh16N15М3Т1 under irradiation, the formation of nanosized particles of intermetallic Ni3Ti precipitates occurs, which intensify recombination of point defects and reduce their accumulation as compared to the steel Kh16Н15М3. As this occurs, the presence of phosphorus in the steel Х16Н15М3Т1 likewise leads to the intensification of the accumulation of vacancy defects.

A comparative study of primary damage state in Ni and NiCr/NiFe with a model grain boundary structure

The interaction of displacement cascades with atomic interfaces, specifically grain boundaries (GBs) is of great importance in design and development of radical advanced Ni-based super alloys with self-healing capabilities for future fission reactors. In this work, pure Ni and NiCr (with 5, 10, 15 and 20 at.% Cr content) and NiFe (with 5, 10 and 15 at.% Fe content) alloys with symmetric tilt Σ5[1 0 0](0 1¯ 3)θ = 37° GBs are used as model structures to study the influence of Cr and Fe on the primary and long-term radiation response of Ni-based alloys with microstructures. Molecular dynamics is used in simulating the primary damage event and the continuous ion bombardments in NiCr/NiFe structures to qualitatively represent the severe irradiation condition expected in next-generation fission reactors. In general, we observe that the GBs in “pristine” and “damaged” (∼after being continuously bombarded) forms preferentially absorb radiation-produced interstitials both Ni and Cr/Fe, over vacancies which results in accumulation and clustering of immobile vacancies in the grain interiors. The presence of Cr and Fe does not significantly affect the sink properties of our model GB and therefore, does not change the clustering behavior of excess vacancies in the bulk grains on picosecond (ps) timescale. The only evident phenomenon is a notable variation in the energetics and probably kinetics of point defects that slightly changes the evolution pattern of displacement cascades in the damage regions on ps timescale. The GB roughening incident is also observed in both Ni and NiFe/NiCr alloys during irradiation. In alloys with GBs, we also analyzed changes in the short range order parameter of irradiated structures. Our results indicate that in the primary event of radiation damage, a single bombardment is not enough to induce any trend in ordering or disordering of Cr and Fe solutes; in a prolonged irradiation, on the other hand, MD results reveal a very weak tendency of solutes to diffuse toward each other, although we did not observe any obvious Cr or Fe clustering in any of the performed displacement cascade simulations. Eventually, on ps timescale, we conclude that the Cr and Fe solutes contribute in enhancement of radiation tolerance of binary alloys in similar ways as Ni atoms do; but further details about the diffusion mechanisms of solutes on a longer timescale is essentially required to have more accurate predictions from a radiation damage perspective.

Controllable dynamics of oxygen vacancies through extrinsic doping for superior catalytic activities.

Due to its strong redox ability, high stability, cost effectiveness and non-toxicity, cerium oxide (CeO2) has been extensively researched as an active photocatalyst material. The underlying photocatalytic reactions are mostly associated with the transportation of oxygen ions through vacancies, but the actual transport phenomenon had not been clearly understood. In this work, gadolinium (Gd) is sequentially doped into CeO2 to investigate how extrinsic doping can modulate oxygen vacancies in CeO2 and influence photocatalytic activities. From our investigations, it was found that the Gd doping may induce structural symmetry breaking leading to a pure CeO2 fluorite structure that transforms mobile oxygen vacancies into clustered or immobile vacancies. When the vacancies were set as "mobile" (for Gd doping levels ≤15 at%), maximum photocatalytic activities were obtained. In contrast, suppressed photocatalytic efficiencies were noted for higher Gd doping levels (20 at% or more). The results reported in this research may provide an extra degree of freedom in the form of extrinsic doping to configure the oxygen vacancy defects and their mobility to achieve better catalytic efficiencies.

Evolution pattern of collision cascades in bcc V with different grain boundary structures: an atomic scale study

In this paper, by means of atomic-scale simulations, we investigate modifications of the evolution pattern of collision cascades in bcc vanadium (V) with different grain boundary (GB) structures on picosecond (ps) timescale. In primary damage state, in agreement with previous results of bcc and fcc bi-crystals, we find that the GBs in V are biased towards interstitials. The biased absorption of interstitials over vacancies reduces the in-cascade annihilation of vacancy-interstitial pairs and leads to aggregation of more number of vacancies in the grains interiors. The sessile vacancies accumulate in the bulk and form immobile vacancy clusters; in contrast, the glissile interstitials disperse in the damage zone and mostly diffuse in the form of single self-interstitial atoms (SIAs)/di-interstitials towards the GB region. Moreover, meanwhile, as we discuss the mechanisms that reduce (or increase) the concentration of defects in bi-crystal structures on picosecond timescale, we study the energetics of defects in close vicinity of pristine GBs, as an alternative driving force that facilitates formation and accumulation of defects in the GB regions. Finally, in a prolonged irradiation, we examine stability and sink properties of the damaged GBs. The results reveal that, irrespective of GB structure, the presence of grain boundaries leads to aggregation of more number of vacancies in the grain interiors in continuous bombardment. Overall, based on the results obtained in the primary damage event and the prolonged irradiation, we conclude that the GBs in bcc V act as efficient defect sinks on the simulated time frame.

Defect interactions with stepped CeO₂/SrTiO₃ interfaces: implications for radiation damage evolution and fast ion conduction.

Due to reduced dimensions and increased interfacial content, nanocomposite oxides offer improved functionalities in a wide variety of advanced technological applications, including their potential use as radiation tolerant materials. To better understand the role of interface structures in influencing the radiation damage tolerance of oxides, we have conducted atomistic calculations to elucidate the behavior of radiation-induced point defects (vacancies and interstitials) at interface steps in a model CeO2/SrTiO3 system. We find that atomic-scale steps at the interface have substantial influence on the defect behavior, which ultimately dictate the material performance in hostile irradiation environments. Distinctive steps react dissimilarly to cation and anion defects, effectively becoming biased sinks for different types of defects. Steps also attract cation interstitials, leaving behind an excess of immobile vacancies. Further, defects introduce significant structural and chemical distortions primarily at the steps. These two factors are plausible origins for the enhanced amorphization at steps seen in our recent experiments. The present work indicates that comprehensive examination of the interaction of radiation-induced point defects with the atomic-scale topology and defect structure of heterointerfaces is essential to evaluate the radiation tolerance of nanocomposites. Finally, our results have implications for other applications, such as fast ion conduction.

The Role of Point Defects in the Mechanical Behavior of Doped Ceria Probed by Nanoindentation

AbstractThe influence of dopant size and oxygen vacancy concentration on the room temperature elastic modulus and creep rate of ceria doped with Pr4+, Pr3+, Lu3+, and Gd3+, is investigated using a nanoindentation technique. Measurements are conducted with both fast (15 mN s−1) and slow (0.15 mN s−1) loading modes, including a load‐hold stage at 150 mN of 8 s and 30 s, respectively. Based on the data obtained using the fast loading mode, it is found that: 1) the dopant size is a primary determinant of the elastic modulus—the larger dopants (Pr3+ and Gd3+) produce lower unrelaxed moduli which are independent of the oxygen vacancy concentration. 2) The rearrangement of point defects is the major source of room temperature creep observed during load‐hold. Pr3+‐ and Gd3+‐doped ceria display the higher creep rates: due to their large size, they repel oxygen vacancies (VO), thereby promoting the formation of O7–CeCe–VO complexes that are capable of low temperature rearrangement. Lower creep rates are observed for Pr4+‐ and Lu3+‐doped ceria: the former has no vacancies and the latter, immobile vacancies. 3) Nanoindentation is a practical technique for identifying materials with labile point defects, which may indicate useful functionality such as high ionic conductivity, large electrostriction, and inelasticity.

Opportunities and Challenges for Materials Innovation in Nuclear Energy

Materials performance is central to the satisfactory operation of current and future nuclear energy systems. For example, the remarkable improvement in the operation and reliability of Generation-II light water reactors (LWRs) over the past 25 years has been largely associated with improvements in steam generator materials, fuel cladding technology (composition and fabrication), and improved understanding of water chemistry impacts on corrosion and deposition. Future fission and proposed fusion energy systems will be increasingly dependent on advanced structural materials to reliably deliver high performance with favorable safety attributes and acceptable economic cost. In many cases, the proposed operating temperatures are significantly higher than the experience base for light water reactors. This motivates development of structural materials with improved high temperature strength for prolonged operating periods and engineered corrosion resistance for the candidate coolants and other materials in the system. The high radiation fluxes in future nuclear energy systems will require the structural materials to have superior radiation resistance compared to currently available materials. The material performance demands are particularly challenging for the fuel cladding and wrapper of next-generation sodium-cooled fast reactors, where simultaneous resistance to high temperature thermal creep and radiation-induced property degradation up to doses of {approx}100-150 dpa is required. Several strategies can be utilized to develop structural materials with simultaneous high radiation resistance, high strength, good toughness and corrosion resistance, and moderate fabrication cost. There are three general approaches for designing radiation resistance: Nano-scale precipitates or interfaces to produce high point defect sink strength (e.g., oxide dispersion strengthened (ODS) and next-generation ferritic/martensitic steels with high particle densities); purposeful utilization of immobile vacancies (e.g., SiC/SiC ceramic composites); and utilization of radiation-resilient matrix phases (e.g., ferritic instead of austenitic steel matrix, etc.). High-performance steels designed using computational thermodynamics are demonstrating promising capability to produce a high density of highly stable nano-scale precipitates that could serve as efficient point defect recombination centers during irradiation, and also provide good thermal creep strength at high temperatures [1]. Figure 1 shows an example of improvements in high temperature thermal creep properties for a 9%Cr-1%Mo ferritic martensitic steel that was achieved simply by slightly altering the thermomechanical processing procedure. Figure 2 compares the fracture toughness behavior of an advanced ODS ferritic steel before and after low dose neutron irradiation at 300 C [2]. The ductile to brittle transition temperature (DBTT) in the LT orientation remained below -150 C with a shift in the DBTT of about 12 C; the corresponding shift in the DBTT for EUROFER97 (9Cr-2WVTa) ferritic/martensitic steel was about 39 C. Higher dose studies are in progress. It will be important for nuclear energy researchers to continue to closely interact with the broader materials science and engineering community in order to effectively leverage innovations that continue to occur in the broad field of materials science. For example, practical aspects used in the aerospace industry to reduce the time from invention of a new alloy system to code qualification and commercialization could be useful for development of new structural materials for nuclear energy systems. In the future, utilization of emerging advanced manufacturing processes such as additive manufacturing to produce near-net shape parts with precise microstructural control will be of increasing importance to control fabrication costs and to create high-performance fabrication architectures that could not be achieved using conventional fabrication methods. Following the accident at the Fukushima Daiichi site in Japan, there is increasing interest in exploring accident tolerant or enhanced safety margin fuel systems for existing and future reactors, which could potentially provide increased response time or reduced consequences via reduced enthalpy production, reduced hydrogen production, and delayed clad rupture or fission product release during a loss of coolant accident compared to conventional Zr alloy cladding/ monolithic UO{sub 2} fuel systems. Although all alternative fuel systems have technological or neutronic shortcomings, exploratory research would be useful to quantify their potential improved accident tolerance so that an informed decision on the best option(s) for future LWR fuel systems can be reached. If research results on a particular accident tolerant concept prove to be promising, it might be possible to initiate confirmatory tests in commercial reactors within about 10 years. (authors)

Spectroscopic differentiation between O-atom vacancy and divacancy defects, respectively, in TiO 2 and HfO 2 by X-ray absorption spectroscopy

Defect state features have been detected in second derivative O K edge spectra for thin films of nano-crystalline TiO 2 and HfO 2. Based on soft X-ray photoelectron band edge spectra, and the occurrence of occupied band edge 4f states in Gd(Sc,Ti)O 3, complementary spectroscopic features have been confirmed in the pre-edge (<530 eV) and vacuum continuum (>545 eV) regimes of O K edge spectra. Qualitatively similar spectral features have been obtained for thin films of HfO 2 and TiO 2, and these have been assigned to defect states associated with vacancies. The two electrons/removed O-atom are not distributed uniformly over the TM atoms defining the vacancy geometry, but instead are localized in equivalent d-states: a d 2 state for a Ti monovacancy and a d 4 state for a Hf divacancy. This new model for electronic structure provides an unambiguous way to differentiate between monovacancy and divacancy arrangements, as well as immobile (or fixed) and mobile vacancies.

Electrical conductivity of TiO2 within n–p transition Part I – Verification of defect disorder model

The present paper reports semiconducting properties and the related defect disorder for undoped TiO2 single crystal using measurements of the electrical conductivity. Isothermal changes of the electrical conductivity as a function of oxygen activity were determined within oxygen activities ranging between 10 Pa and 75 kPa and temperatures between 1073 and 1323 K. The electrical conductivity data, involving both n and p type regimes, are considered in terms of defect disorder assuming that the predominant mobile defects are oxygen vacancies, which are compensated by immobile titanium vacancies. Application of this model led to the determination of the electrical conductivity components related to electrons, electron holes and ions. The determined empirical relationships between electrical conductivity and oxygen activity may be used for predicting the effect of experimental conditions on semiconducting properties of TiO2. The activation energy for the standard conductivity component of electrons and holes is 226 and 102 kJ mol−1 respectively.

The stress anomaly in FeAl–Fe 3Al alloys

The anomalous stress peak observed near 500–600 °C in Fe–Al alloys has now been convincingly explained using a model of hardening by immobile thermal vacancies on the lower temperature side of the peak and the loss of hardening as these vacancies become mobile at higher temperatures. The large numbers of vacancies required for such hardening are associated with compositions close to stoichiometry, i.e. 40–50%Al, raising the question of whether such a vacancy hardening model can be adopted for Fe 3Al alloys, which show a similar stress peak anomaly. Examination of data on vacancy formation over the entire range of composition, Fe–Fe 3Al–FeAl, shows that, indeed, a vacancy hardening model appears capable of explaining the stress anomaly for both FeAl and Fe 3Al.

Classical nucleation theory of microstructure development under cascade-damage irradiation

Cascade irradiation produces a significant fraction of the damage in the form of small mobile and immobile vacancy and interstitial clusters. This has led to the introduction of the Woo–Singh production bias theory. In the pursuant studies, the predominant effort that has been spent is in investigating the validity of the concept, and in its usefulness in complementing the traditional theory based on the concept of sink bias. Although plenty of theoretical and experimental results supports the concept, relatively little attention has been paid to the important area of microstructure nucleation. Within the framework of the classical theory of nucleation of overcritical precipitates from small subcritical nuclei, the nucleation processes at elevated temperatures of both voids and interstitial loops from the primary clusters are similar, and can be similarly treated. Recognizing the importance of stochastic fluctuations in the evolution of small embryos, a single-component nucleation theory is formulated using the Fokker–Planck equation, to take into account the stochastic effects of the fluxes of mobile defects, arising from the random nature of diffusion jumps and cascade initiation. Analytic solutions for the separate cases of voids and Frank loops are obtained, and the corresponding effects on the evolution of the microstructure are discussed.

Evolution of Ar+-damaged graphite surface during annealing as investigated by scanning probe microscopy

The surface evolution of highly oriented pyrolytic graphite irradiated with Ar+ ions of 1.0 keV at doses between 5×1011 and 1×1013 ions/cm2 during annealing was investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in the tapping mode. Hillocks were observed by both STM and AFM after ion irradiation, where the height of a hillock measured by STM was larger than that measured by AFM. The ion-irradiated surface was recovered in three stages during annealing: the first stage at 473–873 K, the second stage at 873–1473 K, and the third stage at 1473–1873 K. In the first stage, many of the ion-induced hillocks recovered rapidly and irregular domelike protrusions were formed due to both the recombination of the mobile interstitial clusters with the immobile vacancies and the aggregation of interstitial clusters. In the second stage, the hillocks recovered slightly and domelike protrusions aggregated to larger domelike protrusions. In the third stage, the hillocks recovered completely and domelike protrusions changed from irregular shapes to regular circles with monatomic step height of graphite due to the change from irregular carbon interstitial clusters to complete extraplane in graphite. Hexagonal hollows were also formed and became larger circular hollows above 1623 K with monatomic step height of graphite due to the vacancy clusters formed by the migration of vacancies and the following collapse of the neighboring layers in graphite.

Comparison of a microstructure evolution model with experiments on irradiated vanadium

A kinetic rate theory model, which includes the formation of cascade-induced clusters (CIIC), is presented. Comparison of the model to ion irradiation data on vanadium reveals the effects of helium generation and cascade-induced interstitial and vacancy clusters on microstructure evolution. The model is based on a simplification of hierarchical rate equations for the clustering of helium bubbles, immobile vacancy clusters, glissile interstitial clusters, sessile dislocation loops, as well as precipitates and grain boundaries. The model shows that the transport of helium to dislocations, bubbles and grain boundaries is strongly transient because of coupling between the nucleation and growth modes of bubble evolution. Helium agglomeration in vacancy clusters is shown to reduce the excess vacancy flux to grow matrix and precipitate-affixed bubbles. The direct formation of vacancy and interstitial clusters in cascades reduces the growth rate of bubbles, and leads to enhanced nucleation of matrix bubbles. In addition to the dislocation and production bias mechanisms, a new mechanism of `helium nucleation bias' is shown to exist under high helium generation rates.

Localized spins and vacancies in the two-dimensionalt-J model

Motivated by recent experimental studies on the effects of Zn and Ni impurities on transport and magnetic properties of cuprate superconductors, we examine how the electronic states of doped two-dimensionalt-J model are affected by the presence of various types of an impurity site. We use an exact-diagonalization technique on small clusters to calculate the ground state properties, single-particles excitation spectra, and spin excitation spectra, where the impurity is introduced as either an immobile vacancy site simulating Zn2+ or a localized spin site withS=1/2 or 1 simulating Ni2+. Possible experimental relevance of the calculated states of doping holes is considered.