MnS Phase Research Articles

A systematic evaluation of physiochemical properties and solar-driven photocatalytic activity of nanosized Mn doped CdS on Methylene Blue dye

Manganese ions were incorporated into CdS nanosystem using wet chemical protocol at different pH values namely 9.0,10.0 and 11.0 and the same were used for photocatalytic degradation of Methylene blue (MB) dye via adsorption phenomena. Several standard analytical techniques were employed to analyse the synthesized nanocompounds: XRD, scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, UV-Vis absorption spectroscopy, Fourier transform infrared spectroscopy, and vibrating-sample magnetometry. The structural analysis revealed the presence of primary cubic zinc blende structure with secondary phases. The morphological studies confirmed the formation of nanostructured particles for all pH values, amongst, pH 10.0 grown particles were showing less agglomeration and better particle stabilization. The TEM analysis confirmed the particle size of 23 nm. The absorption edge and its position shown by UV-Vis absorption analysis exhibited a broad envelope and strong blue shift due to an uneven size distribution and nanodimensional state formation of particles, respectively. The elevation to superparamagnetic state from native diamagnetic state of CdS due to Mn ions incorporation was confirmed by VSM studies. The dual phase composition significantly enhanced the photocatalytic efficiency by improving charge separation and extending light absorption. The MnS phase effectively trapped electrons, reduced recombination rates and facilitated the generation of reactive species. The photocatalytic degradation of methylene blue dye was more efficient (88.87 %) under direct sunlight exposure. Additionally, the enhanced surface properties and adsorption characteristics, as confirmed by the Freundlich isotherm and intraparticle diffusion model, contributed to the superior degradation performance.

Formation of Oxides and Sulfides during the Welding Process of S700MC Steel by Using New Electrodes Wires.

To receive a high-quality welding structure of high-strength S700MC steel for applications in the automotive industry, newly developed electrode wires with increased silicon and manganese content were used. The strength and structural tests of the obtained joints were performed. In the weld, we identified the beneficial oxides strengthening the joint structure and unfavorable MnS inclusions. The non-metallic inclusions were formed inside the weld. Their arrangement, morphology, and chemical composition is described. A view on the high-temperature mechanisms of the formations included during the welding process with new electrode wires is presented. It was found that the dominant mechanism of the inclusion formation and the temperature of the welding process impact the content and varied morphology of inclusions, thus determining the exploitation time of the welded joints obtained. The obtained MAG joints made S700MC steel, due to the formation mainly of oxide inclusions and a relatively small amount of MnS phase, were characterized by a high value of yield and tensile strength, which makes them a promising solution for the automotive industry, especially against the background of connections from the discussed steel grade presented in the literature.

Recycling the Spent LiNi1- x - yMnxCoyO2 Cathodes for High-Performance Electrocatalysts toward Both the Oxygen Catalytic and Methanol Oxidation Reactions.

The traditional recycling methods of the spent lithium ion batteries (LIBs) involve the intricate and cumbersome steps. This work proposes a facile method of acid leaching followed by the sulfurization treatment to achieve the high Li leaching efficiency, and obtain high-performance multi-function electrocatalysts for oxygen reduction (ORR), oxygen evolution (OER), and methanol oxidation reactions (MOR) from the spent LIB ternary cathodes. By this method, the Li leaching efficiency from the spent LIB ternary cathode can reach 98.3%, and the transition metal sulfide heterostructures (LNMCO-H-450S) consisting MnS, NiS2, and NiCo2S4 phases can be obtained. LNMCO-H-450S shows the superior bifunctional oxygen catalytic activities with ORR half-wave potential of 0.763V and OER potential at 10mA cm-2 of 1.561V, surpassing most of the state-of-the-art electrocatalysts. LNMCO-H-450S also demonstrates the superior MOR catalytic activity with the potential at 100mA cm-2 being 1.37V. Using LNMCO-H-450S as the oxygen catalyst, this work can construct the aqueous and solid-state zinc-air batteries with high power density of 309 and 257mW cm-2, respectively. This work provides a promising strategy for the efficient recovery of Li, and reutilization of Ni, Co, and Mn from the spent LIB ternary cathodes.

Thermodynamic Formation and Three-dimensional Characterization of MnS–MgAl<sub>2</sub>O<sub>4</sub> Composite Inclusions in Steel

The distribution and morphology of inclusions in steel have an important effect on the quality of steel. It has been proved that the oxide inclusions can be modified into small and dispersed spinel inclusions by adding proper amount of Mg in steel. The MnS-MgAl2O4 composite inclusions are formed with the core of MgAl2O4 inclusions during the solidification process of molten steel, which has deforming ability and can improve the properties of materials steel. However, the investigation of the control of the composite inclusions is limited by the lack of understanding structure of the inclusions. In this study, the Mg treated steel samples were prepared by induction furnace in this study. In the experiment, SEM-EDS was used to characterize the samples, and thermodynamic calculations were used to describe the evolution mechanism of inclusions and MnS-MgAl2O4 composite inclusions formed in steel samples with different Mg contents. The atomic mismatch calculated between MnS and MgAl2O4 proves that they can nucleate effectively. The three-dimensional (3D) morphology of the composite inclusion of MnS-MgAl2O4 in steel samples were observed by using the X-ray Micro-CT in the beamline of BL16U2 at Shanghai Synchrotron Radiation Facility (SSRF). It is proved that MnS and MgAl2O4 phases exist in the form of co-associated, which is valuable for the control of composite inclusions in steel. The current work provide a powerful method to analyze the detailed structure of the composite inclusions in the steel.

One-Pot Hydrothermal Synthesis of SnMnS Nanosheets for Dielectric Energy Storage Applications

Recently, dielectric materials with high energy storage capacity, low loss, and good temperature stability are highly desired for the rapidly growing field of power electronics. In the current work, we have investigated the change in electrical, optical, and dielectric properties by varying the concentration of compositional elements Sn and Mn. We have prepared the Sn1–xMnxS (0.1, 0.3, 0.5, 0.7, and 0.9) matrix by using the simple single-step hydrothermal method. The samples show that the reflectance percentage increased with the increase of the Mn amount in the composition. The samples exhibit narrow band gap values, which further increase with the Mn content. The band gap value increases from 0.43 to 0.56 eV. The structural analysis shows that the prepared samples are polycrystalline in nature, having SnS and MnS phases. Furthermore, the crystallite sizes increase with an increase in Mn addition, whereas dislocation density and strain decrease simultaneously. The refractive index is calculated from optical band gap values by using the Dimitrov and Sakka equation. The morphological study reveals the uniformity in size and shape of the prepared composition throughout the sample. The presence of compositional elements Sn, Mn, and S is confirmed by EDX analysis. The electrical study reveals that the sample shows good electrical properties, which increase with the Mn contents. The dielectric behavior as a function of frequency and temperature was investigated, and the parameters like dielectric constant, AC conductivity, impedance spectroscopy, and electric modulus were deeply analyzed. All the above optical, electrical, and dielectric properties of the SnMnS matrix have potential use in the field of electronic and energy storage device applications.

Diffusion behavior of bismuth in eco-friendly Bi–S based free cutting steel at high temperature

Deformation cracks during continuous casting and hot rolling are easy to occur in the Bi–S based free cutting steel, and the cracks are related to the diffusion of bismuth. The diffusion behavior of bismuth in the steel and the effect of the microstructure and alloying elements were studied by the diffusion annealing experiment combined with SEM, EDS and TEM analysis. The results show that the bismuth tends to diffuse along the grain boundaries (GBs) and the interfaces between the MnS phase and steel matrix, and then enrich to form the bismuth phases. The bismuth phases with lower melting point would be in liquid form at high temperature and resulted in the cracks along the GBs and interfaces. The bismuth diffusion is more likely to occur toward the parallel rolling direction than the vertical rolling direction in the steel because of the pearlite and MnS phases with the long strip shape and banded distribution. The addition of boron and titanium has the effect of inhibiting the diffusion of bismuth in the steel, which is mainly attributed to the faster diffusion rate of boron and the priority to occupy the defect sites of the GBs and the interfaces between the MnS phase and steel matrix.

Electron-Beam- and Thermal-Annealing-Induced Structural Transformations in Few-Layer MnPS3.

Quasi-two-dimensional (2D) manganese phosphorus trisulfide, MnPS3, which exhibits antiferromagnetic ordering, is a particularly interesting material in the context of magnetism in a system with reduced dimensionality and its potential technological applications. Here, we present an experimental and theoretical study on modifying the properties of freestanding MnPS3 by local structural transformations via electron irradiation in a transmission electron microscope and by thermal annealing under vacuum. In both cases we find that MnS1-xPx phases (0 ≤ x < 1) form in a crystal structure different from that of the host material, namely that of the α- or γ-MnS type. These phase transformations can both be locally controlled by the size of the electron beam as well as by the total applied electron dose and simultaneously imaged at the atomic scale. For the MnS structures generated in this process, our ab initio calculations indicate that their electronic and magnetic properties strongly depend on both in-plane crystallite orientation and thickness. Moreover, the electronic properties of the MnS phases can be further tuned by alloying with phosphorus. Therefore, our results show that electron beam irradiation and thermal annealing can be utilized to grow phases with distinct properties starting from freestanding quasi-2D MnPS3.

In Situ Observation on the Heterogeneous Nucleation of MnS in Heavy Rail Steels with Varied Aluminum Content

In situ observation, scanning electron microscope/energy‐dispersive spectrometer detection, and lattice disregistry calculation are combined to investigate the evolution mechanism of inclusions in heavy rail steels with varied aluminum contents from SiO2–Al2O3–MnO to SiO2–Al2O3–MnO–MnS at 1323 K and 1393 K. The precipitation of MnS inclusions on SiO2–Al2O3–MnO inclusions in the steel occurs when the Al2O3 content in identical oxide inclusions is 30% at 1393 K and 30%, 40%, and 59% at 1323 K. The MnS outer layer shows visible precipitation from 3 min after heating at experimental temperature. The area fraction of MnS phase in SiO2–Al2O3–MnO–MnS inclusions with varied Al2O3 content at 1323 K decreases in the following order: SiO2–Al2O3 (30%)–MnO &gt; SiO2–Al2O3 (40%) –MnO &gt; SiO2–Al2O3 (59%)–MnO. The precipitation of MnS is prone to occur on the Al2O3‐less region of the SiO2–Al2O3–MnO inclusion. The solubility of Mn and S decreases with decreasing temperature. Lower heating temperature and lower Al2O3 content in SiO2–Al2O3–MnO oxide cores are profitable to the heterogeneous nucleation of MnS due to lower disregistry between MnS with the SiO2–Al2O3–MnO inclusion.

Three-phases Co/Co9S8/MnS heterostructures engineering for boosted ORR/OER activities in Zn–air batteries

Breakthroughs in the design of robust bifunctional oxygen reduction/evolution reaction (ORR/OER) catalysts could put Zn–air batteries performance to the summit but remain full of challenges. In this work, the MnS phase was deliberately introduced into the Mott–Schottky Co/Co9S8 for engineering a three-phases Co/Co9S8/MnS heterojunction on defect-rich N-doped mesoporous carbon substrate (Co/Co9S8/MnS-NMC). It affords abundant three-phases heterostructure interfaces that effectively accelerate the electron transfer and trigger further electronic structure reconfiguration, thus advancing the bifunctional ORR/OER activities. Benefiting from these structures, the Co/Co9S8/MnS-NMC possesses a half-wave potential of 0.84 V toward ORR and a low overpotential of 330 mV toward OER at a current density of 10 mA/cm2, catching up with those of commercial Pt/C and RuO2 catalysts. It also endows the Zn–air batteries with a good power density, round-trip efficiency, and robust stability over 750 h, showcasing the promising potential in practical applications. This work not only provides a facile strategy to construct the three-phases heterojunction catalysts but also sheds light on developing the efficient and robust nonprecious metal-based bifunctional ORR/OER catalysts.

Precursor Engineering for the Synthesis of Mixed Anionic Metal (Cu, Mn) Chalcogenide Nanomaterials via Solvent-Less Synthesis.

Metal-organic ligands with mixed chalcogenides are potential compounds for the preparation of mixed anionic metal chalcogenide alloys. However, only a few of such ligands are known, and their complexes are not well explored. We have prepared homo- and hetero-dichalcogenoimidodiphosphinate [(EE'PiPr2NH)] (E, E' = Se, Se; S, S; S, Se) complexes of manganese and copper through metathetical reactions. The X-ray single crystal structure of [Mn{(SePiPr2)2N}2] 1 revealed a triclinic crystal system, with a MnSe4 core unit, whereas the crystal structure determination of [Mn{(SPiPr2)(SePiPr2)N}2] 2 indicated a triclinic crystal system with a Mn(S/Se)2 unit. Both metal centers are tetrahedral, with two deprotonated bidentate ligands forming the coordination sphere. The free ligand was found to exhibit a gauche configuration in the solid state. The energies of the various rotamers of dithio-analogue were studied by DFT calculations. The decomposition behavior of complexes with homo- and heterochalcogenides was investigated, and the complexes were employed as single-source precursors to generate manganese and copper chalcogenides through solvent-less melt reactions between 500 and 550 °C. The deposited powders were characterized by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscopy (TEM), and elemental mapping. MnS, MnSe2, and MnSSe phases were obtained from the decomposition of respective manganese complexes. In contrast, the decomposition of copper-based complexes yielded Cu2-xSe and the sulfur-doped Cu3Se2 phase from seleno- and mixed thio/seleno-complexes of Cu, respectively. The morphology ranged from random sheet-like structures to agglomerated platelets, while the selected area electron diffraction (SAED) revealed the crystalline nature of the materials. Depending on the nature of the complex and the temperature, different amounts of phosphorus were present as an impurity in the synthesized products.

First-principles based study of magnetic states and high-pressure enthalpy landscape of manganese sulfide polymorphs

Using first-principles calculations in combination with special quasirandom structure and occupation control matrix methods, we study the magnetic ordering and the effect of pressure on manganese sulfide polymorphs. At ambient conditions, MnS is commonly observed in paramagnetic rock salt structure, but as the temperature decreases at constant pressure, it becomes antiferromagnetic. On the other hand, at room temperature, MnS has shown to undergo structural transformations as pressure increases. Here, we show that our approach involving the ordering/disordering of the local magnetic moments in addition to the explicit control of the localization of the Mn d-electrons produces energy bandgaps and local magnetic moments in excellent agreement with those observed experimentally, particularly for paramagnetic MnS. Finally, we focus on how MnS evolves under pressure, and from its enthalpy landscape, we identify at about 21 GPa, the structural transformation from rock salt to orthorhombic MnP-type. This structural transformation resembles closely experimental results in which a new stable but unidentified MnS phase was previously reported.

Intimately-coordinated carbon nitride-metal sulfide with high π-d conjugation for efficient battery performance

In this investigation, a hybrid of metal sulfide and carbon nitride (CN) is synthesized by in-situ chemical conversion between metallic species and a single precursor of carbon, nitrogen and sulfur elements through a strong π-d conjugation approach. It is observed that the local chemical alteration in the vicinity of N atom in the CN template triggers the formation of a highly π-conjugated CN system and efficient π-d hybridization at heterointerface. This is accelerated by partial substitution of the Fe atom for Mn ions in the MnS phase which significantly enhances the battery performance, delivering 2031 mA h g−1 after 500 cycles with inverse capacity growth. Via systematic in-depth characterizations, it is found that the gradual increase of Li-ion diffusion coefficients and charge transfer kinetics for repeated cycling is ascribed to the highly dispersed and uniform particles that are confined within the CN template through a strong π-d hybridization.

Effect of sulfur deficiency on the structural, optical and electronic properties of MnS nanostructures

In the current work, the effect of sulfur deficiency on the structural, optical and electronic properties of MnS nanostructures has been investigated. Non-stoichiometric MnS nanostructures (MnS1−x, x = 0, 0.03 and 0.05) samples were synthesized via thermolysis procedure. X-ray diffraction technique using Rietveld refinement procedure was used to identify the different phases percentages, average crystallite size and lattice parameters in different samples. The effect of sulfur deficiency on the different vibrational bands of MnS1−x was explored using Fourier transform infrared (FTIR) technique. UV–visible diffused absorption technique was applied to investigate the absorption, refractive index and optical conductivity of the samples. The energy gap of the system reveals a nonlinear optical bowing effect. Nano MnS1−x semiconductor shows a UV–visible spectra emission depending on Mn to S ratio in the prepared sample. Different electronic parameters (extinction coefficient, dielectric constants, absorption coefficient, refractive index and energy loss function) for (α, β and γ) stoichiometric and non-stoichiometric MnS phases are also explored using the density functional calculation (DFT) and correlated with the obtained experimental results.

Phase control of manganese sulfides during hydrothermal synthesis and their photocatalytic activity for H2 generation

We report a simple method to control phase formation in manganese sulfides during hydrothermal synthesis from aqueous solutions of manganese nitrate and thioacetamide without any additives or surfactants. In this work, MnS2, MnS or MnS2/MnS composites were obtained by adjusting the proportion of thioacetamide in the initial precursor mixture. The photocatalytic activities evaluated by H2 generation under ultraviolet light showed that MnS phase was found to be more active than the MnS2.

Correlation between structural and optical characteristics upon changing the composition ratio of CuS@MnS nanocomposites

Nanocomposite (1 − x)CuS/(x)MnS samples (x = 0, 0.25, 0.5, 0.75, 1) were prepared by a simple thermolysis procedure at low temperature (250 °C). HighScor plus program and Rietveld profile method revealed that CuS crystallized in hexagonal phase, while MnS crystallized in hexagonal and cubic phases. The intermediate alloying ratios (x = 0.5, 0.75) have a cubic phase of MnS and a hexagonal phase of CuS, while sample with x = 0.25 has a hexagonal phase of CuS only. The phase percentage of MnS phase in the nanocomposite samples is always less than the nominal value proposed during the sample’s preparation. The MnS phase in the intermediate alloying ratios (x = 0.5, 0.75) has a larger crystallite size than the CuS phases. Composite samples (x = 0.5, 0.75) revealed two optical band gaps while sample with x = 0.25 showed only one optical band gap. The photoluminescence intensities for CuS@MnS nanocomposites were decreased as compared with either CuS or MnS samples. Nanocomposite (1 − x)CuS/(x)MnS samples emitted UV, violets, blue, green and yellow colors depended on the ratio between CuS and MnS mounts in the composite samples and the excitation wavelengths uses. The different kinds of defects in different samples were investigated also in detail.

Influence of Hot Deformation and Precipitates on the Recrystallization of Nb-V-Ti Free-Cutting Steel

Nb, V, and Ti were added to free-cutting steel to improve its mechanical properties by means of precipitation strengthening and fine grain strengthening. The process parameters during the hot deformation of Nb-V-Ti free-cutting steel were studied at strain rates of 0.01–10 s−1 and temperatures of 850–1250 °C. The isothermal compression test results showed that the temperature rise at low deformation temperature and high strain rate has a great influence on the softening of the steel. The processing maps at strains of 0.3–0.6 were established based on a dynamic material model (DMM). When the strain was 0.6, the optimum hot-working window was at a temperature in the range of 1150–1250 °C and at a strain rate in the range of 0.01–0.1 s−1. The instable regions were mainly located at low temperature and high strain rate. The instable characteristics included the mixed grains around the MnS phase, flow localization, and intense deformation. In general, the existence of MnS leads to a decrease in the toughness of the steel. The MnS phase was easy to be broken when the compression tested at a lower temperature, e.g., 850 °C and at a higher strain rate, e.g., 10 s−1; its morphology changed from a long-rod shape to a discontinuous shape, and then, to a dot-like shape with the decrease in temperature from 1250 to 850 °C and the increase in strain rate from 0.01 to 10 s−1. The nucleation mechanism of this steel was grain boundary bulging. The size of fine (Nb,Ti) (C,N) precipitates is less than 10 nm, inhibiting austenite recrystallization and leading to austenite strengthening during hot deformation at 850 °C. Moreover, the dislocation motion and grain boundary migration were greatly inhibited by the Ti-rich(C,N) and MnS throughout the entire hot deformation process.

Cracking of Copper Brazed Steel Joints Due to Precipitation of MnS upon Cooling

The process of brazing of different steel grades by pure liquid copper foil was studied to reveal the critical conditions when cracks do or do not appear in the braze upon cooling without any external load. Steel grades C45 (S 0.030 wt.%, no Mn and no Cr), S103 (Mn 0.25 wt.% and S 0.020 wt.% with no Cr), CK60 (0.75 wt.% Mn, 0.07 wt.% S and 0.15 wt.% Cr) and EN 1.4034 (Cr 12 wt.%, Mn 1.0 wt.% and S 0.035 wt.%) are studied under identical conditions using copper foils of 70-microns-thick. The samples were held above the melting point of copper at 1100 °C under high vacuum for different time durations (between 180 and 3600 s) and then cooled spontaneously. The joints were found cracked during cooling after a certain critical holding time. This critical holding time for cracking was found to decrease with increasing the Mn content and the S content of steel. It is observed that cracking is due to the precipitation of a critical amount of MnS phase upon cooling. The MnS/Cu interface is the weakest interface in the joint (with adhesion ensured only by van-der-Waals bonds), which is broken/separated upon cooling due to difference in heat expansion coefficients of the sulfide and copper phases. Higher is the Mn and S content, shorter is the probable time required for crack to appear in the joint. The braze integrity diagram is constructed as function of solubility product of MnS in steel and holding time showing a stable crack-free technological region and an unstable technological region with high probability of crack formation.

Effect of composition ratio on the structural and optical properties of MnS@ZnS nanocomposites

Nanocomposites (1−x)MnS‒xZnS (x = 0, 0.25, 0.5, 0.75, 1) heterostructures were synthesized by a simple chemical procedure at low temperature (300 °C). The influence of the alloying ratio (x) on the phases developed was investigated utilizing the Rietveld X-ray diffraction (XRD) analysis and Fourier transform infrared (FTIR). Zinc sulfide crystallized in one phase having zincblende structure, while manganese sulfide was formed in three phases having cubic and hexagonal structures. The determined crystallite size for ZnS was in the range 3–4 nm, resembling quantum dots, while for the cubic MnS phase the size was bigger in the range 15–20 nm, and it is much bigger for MnS hexagonal phase, about 76 nm. A High-resolution transmission electron microscope (HRTEM) images confirmed the big difference in particle sizes of MnS and ZnS. The UV diffused reflectance was obviously affected by the ratio of MnS to ZnS in the matrix; the intermediate composites (0.25, 0.5, and 0.75) had bandgap energy less than those of pure MnS and ZnS. The refractive index value was influenced by the degree of crystallinity and density of the samples. Photoluminescence (PL) analysis revealed high dependence on the sample composition with ZnS and the intermediate composites samples had broader spectra compared to the MnS sample; the intermediate samples were blue shifted. Also, PL intensities of intermediate nanocomposites were less than those of MnS and ZnS samples.

Sulfide Transformation from Self-Lubricating to Free-Cutting in Powder Metallurgy Iron-Based Alloys

In this study, the effects of sulfide transformation on mechanical properties and microstructure in Fe-Cu-C alloys were investigated. Taking advantages of self-lubricating and free-cutting of different sulfides, the sulfide transition in iron-based alloys mainly included two parts. Firstly, a thin layer of FeS film was coated on the iron powder surface during annealing, acting as solid lubricant to reduce the compaction friction. Then, in situ MnS with particle size of 1-2 μm was formed followed by the reaction of FeS and Mn during sintering. Consequently, the sintered density reached to 7.34 g/cm3 and the machinability significantly improved with less tool wear. Besides, the mechanical performance was also enhanced. The hardness increased from 80.5 HRB to 84.1 HRB, and the tensile strength increased from 590 to 631 MPa. The MnS phase was mainly distributed along the grain boundaries.

Effect of manganese dopants on defects, nano-strain, and photovoltaic performance of Mn–CdS/CdSe nanocomposite-sensitized ZnO nanowire solar cells

This study reports the mechanism of power conversion efficiency (PCE) enhancement in CdS/CdSe quantum dot (QD) composite-sensitized ZnO nanowire (NW) solar cells when Mn2+ ions are doped in CdS QDs. Various ZnO NWs sensitized with different types of QD-composites including CdS, CdS/CdSe and Mn–CdS/CdSe QDs were successfully synthesized using an in-situ sequential assembly process involving successive ionic layer adsorption and reaction and chemical bath deposition at room temperature. QD solar cells with a ZnS/CdSe/Mn(0.02M)-CdS/ZnO NW structure exhibited a PCE of 3.47% (Voc = 0.74 V, Jsc = 14.56 mA/cm2, and FF = 36.92%), which is 33% higher than that (2.61%) of their counterparts without Mn2+ dopants. Electrochemical impedance spectroscopy studies of the devices reveal that the main role of the Mn2+ dopant was to reduce the recombination of photo-excited carriers. Similar improvement in PCE is traditionally indicated as being a result of the generation of the mid-band (4T1−6A1) region owing to the atomic d orbitals of Mn (4T1 and 6A1); however, no evidence is available. Rather, we focused on quantifying the nanoscale strain in the QD composites with and without Mn2+; this is because the formation of nanoscale strain in QDs implies the presence of considerable imperfections functioning as charge traps and recombination centers. Analyses of the interface, interior, and crystallinity of the QDs by using high-resolution electron microscopy combined with geometric phase analysis (GPA) revealed that Mn2+ doping significantly reduced the lattice nano-strain in the QD nano-composites. This result is probably owing to Mn2+ cation diffusion (or exchange) to the defective CdS/CdSe layer assisted by the differences among the solubility products (Ksp) in the MnS, CdS, and CdSe phases; this diffusion reduces the nanoscale strain resulting from the presence of defects and misfit dislocations in QD composites and thereby decreases carrier recombination.