The halogen-substituted derivatives and the parent aniline tetramer as organic semiconductors have been theoretically investigated with a focus on the electronic properties and charge transport properties through density functional theory and Marcus–Hush theory methods. The study on the transport properties of holes and electrons can obtain insight into the effect of halogenation substitution on injection of charge carriers and transport character. The equilibrium geometries, reorganization energies, frontier molecular orbitals, intermolecular electronic couplings, electrostatic potential isosurfaces, and angular resolution anisotropic mobilities were calculated. The calculated results revealed that perfluorination and perchlorination can induce stronger structure relaxation and effectively lower the highest occupied molecular orbital and lowest unoccupied molecular orbital levels. The angle dependence mobilities of the three crystals show remarkable anisotropic character. The carrier mobility curves for both electron and hole transport of the parent aniline tetramer and halogen-substituted derivatives all show a remarkable anisotropic feature. Furthermore, the ANIH and ANICl crystals show higher electron-transfer mobilities than hole-transfer mobilities and, hence, perform better as an n-type organic semiconductor. The ANIH crystal possesses a low reorganization energy combined with a high electronic coupling and electron-transfer mobility, which indicates that the ANIH crystal might be a more ideal candidate as an n-type organic semiconductor material.

FeSiAl powder (FSA)/water-based varnish (WV) microwave-absorbing coatings with discrete structure (DMCs) were fabricated, and the effects of the discrete structure on their impedance matching and absorption performance were investigated. The electromagnetic parameters of FSA were determined in the frequency range 2–18 GHz using transmission/reflection measurements. The microwave absorption (MA) properties of the coatings were determined by measuring the reflection loss using the arch method. The normalized input impedances of the DMCs with different coatings were calculated for the investigation of impedance matching. The results showed that, compared with conventional coatings, the discrete-structure coating has superior impedance matching and delivers clearly enhanced MA performance. When the concentration of FeSiAl is 17 wt%, the absorption peak reaches −12.5 dB from −5.8 dB, and the qualified frequency bandwidth is 2.5 GHz. Furthermore, the effect of the discrete unit size and coating thickness on the impedance matching and absorption performance of the coatings were investigated.

•The Co doping in δ-MnO2 tends to form interstitial atoms.•The formation of O vacancies is easier than Mn vacancies.•Both impurity atoms and vacancy formation improve the atomic polarizability.•Doping improves the displacement polarizability, while vacancies decrease it.•The presence of crystal defects in δ-MnO2 enhances microwave loss.The δ-MnO2 has a layered structure and is expected to be a good absorbing material. Here, CASTEP was used for a theoretical study of the microwave absorption properties of δ-MnO2 with defects (interstitial and substitutional cobalt atoms, vacancies). The results show that by analyzing the density of states (DOS) and partial density of states (PDOS), the defects change the charge distribution and increase the magnetic moment (increased by about 19 orders of magnitude). The bond length increased from 1.979 Å to 1.980 Å after substitutional defects formed to enhance the displacement polarizability. The changes in the charge distribution increase the atomic polarizability. The presence of crystal defects enhances both the magnetic loss and dielectric loss. In addition, the calculated defect formation energies show that the Co atoms tend to form interstitial atoms in MnO2 (−16.90 eV), and the oxygen vacancy defects (−0.77 eV) are more easily formed than the manganese vacancy (33.14 eV).Download high-res image (58KB)Download full-size image

A facile in situ polymerization process was introduced for the preparation of RGO–PANI hybrids with investigation of their microwave absorbing properties. The structural and morphological characterization were performed using Fourier transform infrared (FTIR), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the hierarchical nanocomposites of aligned polyaniline nanorods grown vertically on the surface of RGO were successfully synthesized. The hybrids with special structure possessed more distinct dielectric response characteristics and better electromagnetic absorption properties than pure PANI. The maximum reflection loss value of the composites is up to −43 dB at 12.4 GHz and the absorption bandwidth exceeding −10 dB is 3.5 GHz with a thickness of 2 mm. The results indicate that hierarchical nanocomposites of aligned polyaniline nanorods on reduced graphene oxide nanosheets are efficient materials for microwave absorption.

The polyaniline water hydrogen-bonded complex was studied by first-principles calculation. The density functional theory method was used to calculate the structure characters, natural bond orbital charge distribution, infrared spectra and the frontier molecular orbital. Results showed that the H–O···H–N and C–N···H–O type intermolecular hydrogen bonds were formed. The bonds involved in the intermolecular H-bond were all influenced by the hydrogen bonding interaction. During the hydrogen bond formation, the polymer chains in the complexes were all charged, which can be an important factor contributing to the increase of electrical conductivity. The N1–H vibration was strongly influenced, and the locations as well as the intensities of N1–H absorption bands were all changed in the complexes. In the orbital transition of HOMO to LUMO, the electron density transferred from benzenoid ring to quinoid ring.

•The excited-state hydrogen-bonding characteristics of PANI were studied.•The hydrogen bonds CN ⋯ HO and NH ⋯ OH can be formed in the complexes.•The hydrogen-bonding strengthening was demonstrated upon photoexcitation.•H-bond strengthening plays an important role in the internal conversion process.A theoretical study was carried out to study the excited-state of hydrogen-bonding characteristics of polyaniline (PANI) in aqueous environment. The hydrogen-bonded PANI-H2O complexes were studied using first-principles calculations based on density functional theory (DFT). The electronic excitation energies and the corresponding oscillator strengths of the low-lying electronically excited states for hydrogen-bonded complexes were calculated by time-dependent density functional theory (TDDFT). The ground-state geometric structures were optimized, and it is observed that the intermolecular hydrogen bonds CN ⋯ HO and NH ⋯ OH were formed in PANI-H2O complexes. The formed hydrogen bonds influenced the bond lengths, the charge distribution, as well as the spectral characters of the groups involved. It was concluded that all the hydrogen-bonded PANI-H2O complexes were primarily excited to the S1 states with the largest oscillator strength. In addition, the orbital transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) involved intramolecular charge redistribution resulting to increase the electron density of the quinonoid rings.

•A kind of discrete structure was applied on coatings to improve the absorption performance.•The effects of absorber content and structure on the absorption properties were studied.•The absorption properties improved with the decrease of discrete patch size.•The equivalent circuit model was constructed to analyze the improvement mechanisms of absorption properties.We fabricated flaky FeSiAl (FFSA) absorption coatings and flaky FeSiAl (FFSA)/carbon black (CB) composite absorption coatings, and studied the effects of a discrete structure on the absorption performance of both coatings. The electromagnetic parameters of FFSA and CB were measured in the frequency range of 2–18 GHz using transmission/reflection technology. We also investigated the electromagnetic loss mechanisms of FFSA and CB. The microwave absorption properties of the coatings were determined by measuring the reflection loss (RL) using the arch method. We then analyzed the effects of the contents and the discrete structure on absorption properties. The results showed that, for the FFSA coatings, discrete structures markedly improved absorption properties. When the discrete unit sizes decreased, the absorption properties increased. The addition of CB further improved the absorption performance of the FFSA absorption coating. And when FFSA/CB composite coatings were cut into discrete structures, the absorption peak values decreased and the absorption peak frequencies shifted toward higher frequency ranges, which were consistent with those of the FFSA coating. Because of the conductivity differences between FFSA and CB, the FFSA/CB composite coatings with discrete structures had significant improvements in absorption. The improved absorption weakened when the CB content achieved a certain value. The equivalent circuit models were built to analyze the improvement mechanisms of absorption properties when the coating was cut into a discrete structure.

•β-MnO2 microncube has been synthesized via a simple aqueous chemical route.•The crystal type changed from γ-MnO2 to β-MnO2 and the morphology changed to a microncube with rectangular pyramid.•The evolution process of the β-MnO2 structure is proposed to involve two main stages.•β-MnO2 has certain dielectric loss properties.•An effective absorption bandwidth of 3.5 GHz was achieved from the β-MnO2/paraffin wax composite.β-MnO2 microncube is a novel morphology of microncube with rectangular pyramid. It has been synthesized for the first time via a simple aqueous chemical route under hydrothermal conditions without any templates. When the reaction time is increased from 1 h to 10 h, the crystal type changed from γ-MnO2 to β-MnO2 and the morphology changed from an urchin-like shape to a microncube with rectangular pyramid. We propose a possible growth mechanism for intrinsic structural growth mechanism, the evolution process of the β-MnO2 structure is proposed to involve two main stages. Besides, the electromagnetic properties of the synthesized β-MnO2 were investigated. It shows that β-MnO2 has certain dielectric loss properties and an effective absorption bandwidth (reflection loss lower than − 10 dB) of 3.5 GHz was achieved from the β-MnO2/paraffin wax composite.

•Co2+, Ni2+ and Co2+/Ni2+ co-doped β-MnO2 were synthesized by hydrothermal reaction.•The crystallographic defects modified the microwave dielectric performance.•The dielectric loss capacity was enhanced after doping of Ni2+ and Co2+.•Mn vacancy was the most important factor in microwave polarization process.Co2+, Ni2+ and Co2+/Ni2+ co-doped β-MnO2 were synthesized by hydrothermal reaction to study the influence of crystal defects on the microwave dielectric response. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), transmission electron microscopy (TEM), and vector network analyzer. The construction of defective β-MnO2, with doping of Co2+ and Mn/O vacancies, was also discussed based on first-principles calculation. Results showed that the crystallographic defects played important role in modifying the microwave dielectric performance. The dielectric loss capacity at 2–18 GHz was enhanced after doping of Ni2+ and Co2+, which was ascribed to the ionic polarization process. In the deficient configurations, the appearance of Mn vacancy narrowed the band gap, forming weak bound electrons and weak contact ions. Then the electronic and ionic relaxation polarization processes took place among these charged particles in the applied field. Mn vacancy was the most important factor in controlling the microwave polarization process, followed by O vacancy and extrinsic Co2+.

First-principles calculations were performed to study the hydrogen bond in the camphorsulfonic (CSA) acid-doped polyaniline system. The density functional theory (DFT) method was used to calculate the ground-state geometric structure optimization. Meanwhile, the electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states were investigated by the time-dependent density functional theory (TDDFT) method. In the acid-doped system, SO⋯H–N type intermolecular hydrogen bonds were formed. The band lengths at the hydrogen bond formation point were elongated, and the stronger hydrogen-bond interaction causes longer bond stretching. DPA–DMSO was photoexcited to the S2 state which possessed the largest oscillator strength, and the ICPA–DMSO was photoexcited to the S3 state in a similar way. In addition, we also discussed the frontier molecular orbitals and the electron density transition.

•The flaky Fe–Co–Ni alloy was prepared by mechanical alloying.•The microstructure and magnetic properties of alloy changed following milling.•Magnetic property was calculated in a theoretical perspective.•Absorbing ability of Fe–Co–Ni alloy was improved after milling.Comprehensive utilization of experimental measurement and quantum-mechanical calculation were implemented to study the properties of Fe–Co–Ni alloy prepared by mechanical alloying using planetary ball mill. The related properties were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), vector network analyzer. Moreover, the theoretical calculation was conducted based on density functional theory (DFT) within the generalized gradient approximation (GGA). The systematical discussions about microstructures, including morphology, phase structure, grain size, internal strain, were carried out. The electromagnetic properties were also talked combining with the microstructure analysis, including saturation magnetization (MS), coercivity (HC), electromagnetic parameter (permeability μ and permitivity ɛ) and microwave reflection loss (RL). Results showed that the above properties changed with the alloying process: α-Fe (Co) powders milling for 25 h had the maximum MS (153 emu/g). The microwave absorbing ability was enhanced with increased milling time, and the minimum RL (−32.4 dB) was obtained at about 9 GHz after milling for 90 h.

The theoretical calculation of polyaniline tetramers were performed in implicit water solvent medium using the polarizable continuum model with density functional theory. In order to explore the protonation mechanism of polyaniline, the geometry characteristics, charge distribution, frontier molecular orbitals (MOs) and stability of emeraldine base and emeraldine salts in tetramer were investigated by B3LYP/6-31G+(d,p), and the significant increase mechanism of the electrical conductivity of polyaniline upon protonation was researched in detail. It was shown that optimized molecular geometry by protonation doping suggested a tendency towards bipolaron delocalization and a greater π-conjugation proved by bond length alternation and the torsional angles. Furthermore, the NBO of ES3 was distributed equably and should be conducive to the electrical conductivity, the frontier MOs were effectively established, and an electronic transition from HOMO to LUMO+1 is turned out to be a ππ* transition finally. In addition, compared with the computed energies of different emeraldine salt configurations, the bipolaronic lattice was taken for the most stable structure.

The microwave electromagnetic properties of Fe-doped α-MnO2 are studied theoretically using quantum mechanical calculations based on density functional theory. The calculations employ the Perdew–Burke–Ernzerhof model, a generalized gradient approximation, to deal with the exchange–correlation interaction. The possible role of Fe doping in modifying the electromagnetic performance is studied utilizing density of states (DOS) and the bond length between the metal and oxygen. Calculations of the bond length in the presence of Fe show a contracted bond length between the metal atoms and O with enhanced bond strength, resulting in increased storage of electric field energy. This explains the experimental observation of a reduced dielectric loss after Fe-doping. The DOS results demonstrate that Fe doping enhances the spin-polarization of MnO2. Therefore, the total magnetic moment is increased after doping, corresponding to the magnetic enhancement of MnO2. The theoretical predictions concluded from the quantum mechanical calculations agree well with the experimental observations. The results provide an early stage exploration of theoretical research on the microwave absorbing properties of doped MnO2.

Carbonyl-iron and Fe91.2Si3.1P2.9Sb2.8 powder used as dual-fillers for thin microwave absorbers were firstly prepared by a simple mechanical mixture technique. The patterns and magnetic properties of carbonyl-iron and Fe91.2Si3.1P2.9Sb2.8 were characterized by scanning electron microscope and vibrating sample magnetometer The electromagnetic parameters were measured in the 2–7 GHz range by a HP8720B vector network analyzer. In comparison with carbonyl-iron and Fe91.2Si3.1P2.9Sb2.8 powder, the carbonyl-iron/Fe91.2Si3.1P2.9Sb2.8 composites powder exhibited excellent microwave absorption properties in the 2–7 GHz frequency range. The reflection loss was found to <−20 dB in the 2–7 GHz range for thickness of 2–5.3 mm, and the minimum reflection loss of −37 dB was observed at 5.2 GHz with a matching thickness of 2.5 mm. The excellent microwave absorption properties were firstly explained by using quantitatively coefficient of electromagnetic matching. In addition, a strong natural resonance was found in the carbonyl-iron/Fe91.2Si3.1P2.9Sb2.8 composites powder as an important reason bringing about the excellent microwave absorption.

A facile redox reaction between KMnO4 and MnSO4 was carried out to investigate the dielectric response and microwave absorbing properties of Ni/Co-doped MnO2. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that the powders were α-MnO2 with one-dimensional nanostructure. The doping of Ni/Co had a certain effect on the dielectric properties: the relative complex permittivity showed a more distinct dielectric response characteristic, and the imaginary part exhibited a great enhancement of 2–18 GHz, which resulted in controllable wave-absorbing properties. The microwave absorbing bandwidth (RL < −10 dB) for Co-doped MnO2 was located at 10.96–16.13 GHz with a thickness of 2 mm. Furthermore, the Debye equation was introduced to explain the novel microwave dielectric response of doped MnO2. Some other properties derived from dielectric performances were also investigated, such as dielectric loss tangent and dielectric conductivity. In particular, first-principles calculations based on density functional theory (DFT) were used to uncover the relationship of electronic structure and dielectric properties on the microscopic scale.

The water atomized Fe87.5Si7Al5.5 (Wt.%) alloy was processed by a high-energy planetary ball-milling. The characterization of morphology, microstructure, and electromagnetic properties were measured by scanning electron microscope (SEM), X-ray diffractometer, vibrating sample magnetometer (VSM), vector network analyzer and the first principle method. The analysis results showed that the powders shape became flaky from fusiform. The powders showed a reduction of the average grain size and the increase of the internal strain, and then presented an adverse variation trend after 55 h milling. The powders that milled 10 h had the largest saturation magnetization MS (131 emu/g). The value μ′ of the powders decreased with increasing milling time at relatively lower frequency (2–8 GHz), but opposite variation tendency happened at higher frequency (8–18 GHz). Also, only short time milling can enhance the value of μ″ in the test frequency. The powders after 10 h milling showed excellent microwave absorption (RL < −10 dB) at the frequency 9.0–15.6 GHz and the absorption peak shifted regularly to the high frequency as the increased milling time. Furthermore, the effect of charge exchange between the Fe and Si on the saturation magnetization in the ball-milling process was also investigated by using density functional theory (DFT) of first principle.Graphical abstractHighlights► The water atomized Fe87.5Si7Al5.5 (Wt.%) alloy was processed by ball-milling. ► The microstructure and magnetic properties of alloy changed following milling. ► The powders milled for 10 h have the largest Ms and strongest reflection loss. ► The permeability of the powders milled for 2 h is the largest. ► The charge exchange between Fe and Si is discussed base on first-principles.

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO2 was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO2 content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO2 and CI weight concentration (SiO2:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO2-free composite coating.

To solve more and more serious electromagnetic radiations, cement-based composites were prepared by introducing porous materials into cement. The reflection losses were studied using arched testing method in the frequency range of 1.7–18 GHz. The results showed that the absorption properties were improved obviously. The mechanisms of wave attenuation of the composites were discussed, which indicated that the scattering and multi-scattering in porous beads played an important role. The filling ratio of porous beads, the bead geometries as well as the conformation of cement all had noticeably influence on the absorption properties. The lowest reflection loss of −22 dB was obtained at 5.6 GHz when the specimen was filled with 50 vol.% expanded polystyrene, and the effective absorption bandwidth (less than −10 dB) reached 10.6 GHz when the specimen was filled with 50 vol.% expanded polystyrene and 2 vol.% carbon black.Research highlights► Cement composites with lower reflection peak and broader bandwidth are developed. ► The role of scattering and multiple scattering in wave attenuation is defined. ► The unusual shift of matching frequency versus the content of porous beads is noticed. ► The influence of bead geometry is discussed.

Fe-doped MnO2 with a hollow sea urchin-like ball chain shape was first synthesized under a high magnetic field of 10 T. The formation mechanism was investigated and discussed in detail. The synthesized samples were characterized by XRD, SEM, TEM, EMPA, and vector network analysis. By doping MnO2 with Fe, the relative complex permittivity of MnO2 and its corresponding loss tangent clearly decreases, but its relative complex permeability and its corresponding loss tangent markedly increases. Moreover, the theoretically calculated values of reflection loss show that with increasing the Fe content, the as-prepared Fe-doped MnO2 exhibits good microwave absorption capability.Graphical AbstractFe-doped MnO2 with a hollow sea urchin-like ball chain shape was first synthesized in a high magnetic field of 10 T via a simple chemical process.Highlights► Fe-doped MnO2 with a hollow sea urchin-like ball chain shape was first synthesized. ► We investigated formation mechanism and electromagnetic properties of the Fe-doped MnO2. ► By doping MnO2 with Fe, the electromagnetic properties are improved obviously.

MnO2 with a sea urchin-like ball chain shape was first synthesized in a high magnetic field via a simple chemical process, and a mechanism for the formation of this grain shape was discussed. The as-synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The dielectric constant and the loss tangent clearly decreased under a magnetic field. The magnetic loss tangent and the imaginary part of the magnetic permeability increased substantially. Furthermore, the theoretically calculated values of reflection loss showed that the absorption peaks shifted to a higher frequency with increases in the magnetic field strength.MnO2 with a sea urchin-like ball chain shape is first synthesized in a high magnetic field via a simple hydrothermal route.

Redoped-polyaniline (PANI) was prepared by chemical redox polymerization of aniline using ammonium perdisulfate, (NH4)2S2O8, as an oxidant and hydrochloric acid, HCl, as a doping agent. The structural characterization based on FT-IR, UV–vis, XRD, TEM and electrical conductivity was first used to evaluate the thermal stability and the electromagnetic properties. The redoped-PANI was partial crystalline nature and similar spherical structure about 4–5 nm in diameter. The redoped-PANI displayed outstanding electric conduction and thermally stability. The volume resistivity was as high as 5.18 × 10−1 Ω cm. Doped-PANI maintained stable conductibility at temperatures up to about 100 °C. The redoped-PANI had excellent dielectric properties, multiple Debye dipolar relaxation, and substantial microwave absorption capability. The values of ɛ′rɛ′r and ɛ″rɛ″r for the redoped-PANI powder were from 9.31 to 5.95 and 3.44 to 2.10, respectively. The maximum reflection loss of redoped-PANI composites of 2.0 mm thickness were −14.3 dB at 16.4 GHz and the effective absorption band under −10 dB was from 10.0 to 13 GHz.

The complex permittivity, permeability and microwave-absorbing properties of rubber composites filled with carbonyl iron are measured at frequencies from 2–18 GHz. The results indicate that the reflection loss peak shifts towards low frequency region with increasing layer thickness or increasing weight concentration. The minimum reflection loss value of −23.06 dB was obtained at 3.3 GHz for the composites with 80% wt. These results show that the composites possess good microwave absorbing ability in both low- and highfrequency bands.

MnO2 powder was synthesized in a high magnetic field (8 T) via a simple route, and the formation mechanism for the grain shape was discussed. The synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The morphology of synthesized MnO2 was sea urchin-like ball chain with a low density center, just like “hollow-like”. Throughout the whole frequency range, the dielectric constant and the loss tangent clearly decreased in 8 T high magnetic field. Moreover, the magnetic permeability and the loss tangent increased slightly in the frequency range 2–13 GHz. Furthermore, the theoretically calculated values of reflection loss showed that when the magnetic field strength 8 T was adopted, the absorption peak became smoother and shifted to a higher frequency.

First-principles calculations were performed to study the hydrogen bond in the camphorsulfonic (CSA) acid-doped polyaniline system. The density functional theory (DFT) method was used to calculate the ground-state geometric structure optimization. Meanwhile, the electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states were investigated by the time-dependent density functional theory (TDDFT) method. In the acid-doped system, SO⋯H–N type intermolecular hydrogen bonds were formed. The band lengths at the hydrogen bond formation point were elongated, and the stronger hydrogen-bond interaction causes longer bond stretching. DPA–DMSO was photoexcited to the S2 state which possessed the largest oscillator strength, and the ICPA–DMSO was photoexcited to the S3 state in a similar way. In addition, we also discussed the frontier molecular orbitals and the electron density transition.

The microwave electromagnetic properties of Fe-doped α-MnO2 are studied theoretically using quantum mechanical calculations based on density functional theory. The calculations employ the Perdew–Burke–Ernzerhof model, a generalized gradient approximation, to deal with the exchange–correlation interaction. The possible role of Fe doping in modifying the electromagnetic performance is studied utilizing density of states (DOS) and the bond length between the metal and oxygen. Calculations of the bond length in the presence of Fe show a contracted bond length between the metal atoms and O with enhanced bond strength, resulting in increased storage of electric field energy. This explains the experimental observation of a reduced dielectric loss after Fe-doping. The DOS results demonstrate that Fe doping enhances the spin-polarization of MnO2. Therefore, the total magnetic moment is increased after doping, corresponding to the magnetic enhancement of MnO2. The theoretical predictions concluded from the quantum mechanical calculations agree well with the experimental observations. The results provide an early stage exploration of theoretical research on the microwave absorbing properties of doped MnO2.