Refrigeration Devices Research Articles

High Performance BiSbTe Alloy for Superior Thermoelectric Cooling

AbstractAt present, the weak thermoelectric and mechanical performance of zone‐melting bismuth telluride alloys cannot support the further improvement of cooling and processing performance of semiconductor refrigeration devices. Here, MnO2 is added into high‐strength Bi0.4Sb1.6Te3 prepared by ball milling method to optimize its thermoelectric transport properties. Via in situ reaction, Sb2O3 nano‐precipitates are formed in the matrix, which also leads to the surplus of Te element. As results, the donor‐like effect is suppressed, thereby increasing carrier concentration and power factor. Besides, volatilization of Te‐rich phases during sintering leaves plentiful nanopores, which together with Sb2O3 nano‐precipitates significantly decrease the lattice thermal conductivity. Eventually, the maximum ZT reaches 1.43 at 75 °C for the Bi0.4Sb1.6Te3+0.01MnO2 sample. On this basis, a 31‐pairs module made of the material and commercial n‐type BiTeSe produces large temperature differences (ΔT) of 70.1, 80.8, and 89.4 K at the hot‐side temperature (Th) of 300, 325, and 350 K respectively, which are highly competitive. The maximum coefficient of performance of 8.6 and cooling capacity of 7 W are achieved when Th is set as 325 K. This excellent progress will promote the further development of bismuth telluride refrigeration modules.

A micro solid-state refrigeration prototype device based on the electrocaloric effect

The increase in chip power consumption and heat generation has created the need for new cooling technologies, and the electrocaloric effect (ECE) has become a promising micro cooling technology due to its high efficiency and environmentally friendly features. In this work, a solid-state refrigeration prototype device based on ECE were designed. We first developed a refrigeration process based on the Brayton cycle. After the structural design, electrocaloric material selection, device fabrication, and assembly, we obtained a miniature solid-state refrigeration prototype device. With a 250-V applied voltage and a 3-s cycle period, this prototype refrigeration device achieved a temperature span (Tspan, difference in temperature between the hot end and the cold end) of 0.46 K between the hot end and cold end at room temperature, providing a new design concept for the ECE in micro cooling technology.

Condition-based maintenance with reinforcement learning for refrigeration systems with selected monitored features

Worldwide, buildings are responsible for almost 30% of energy consumption, and those buildings that intensively use refrigeration systems, such as supermarkets and grocery stores, are also among the most energy-intensive consumers. Refrigeration devices, either commercial or residential, are responsible for a significant part of net emissions. Based on careful measurements, it is possible to reduce energy consumption in these devices by up to 15% only by improving the fault detection and diagnosis techniques. Thus, improving maintenance programs has become a crucial area in energy management in recent years. Nowadays, the market has experienced a hike after smart systems and new network interfaces applied to smart buildings that have allowed previously isolated devices to become smart devices, interacting with control algorithms smartly and, to some extent, autonomously. Here, we propose a reinforcement learning framework to develop a maintenance policy for mechanical compression refrigeration devices. Firstly, a test bench is built in which each component is assigned to be individually repairable and individually degradable in parallel and interconnected processes. Then, the degradation of the components is combined to formulate the system degradation, and the optimal maintenance policy is modeled via Markov decision processes and solved by a reinforcement learning algorithm. The agent-proposed maintenance program if compared to corrective maintenance, managed to reduce energy use and emissions by around 6% while avoiding shortfalls, as well as about the preventive program, where the agent managed to accomplish the same level of energy efficiency while reducing the maintenance costs by 31% and the time under maintenance in 10%. It was found that the reinforcement learning frameworks applied to maintenance have a series of challenges but are innovative and can show promising results compared to traditional maintenance techniques, such as preventive and corrective ones.

Assessment of medicines cold chain storage conformity with the requirements of the World Health Organization in health facilities of the Eastern Province of Rwanda

BackgroundDespite the prominent evidence of cold chain monitoring in the health system to reduce wastage and maintain product potency, there are still inefficiencies in the storage and transportation of cold chain products. This study assessed medicine cold chain storage conformity in health facilities in the Eastern Province of Rwanda.MethodsA cross-sectional and prospective with quantitative and qualitative approaches study was approved, and 44 health facilities (public, faith-based and private) were selected using both convenience, stratified, and purposive sampling techniques. Temperature data loggers were mounted in refrigerators to measure the Mean Kinetic Temperature (MKT).ResultsThe overall performance of cold chain storage conformity of refrigerators assessed was 54 (73.0%). The conformity found in refrigerators of pharmacy stock in public health facilities was 22 (56.0%), in vaccination program was 25 (100.0%), and in private retail pharmacies was 7 (70.0%). The MKT measured fit the required cold chain storage at this rate. Most refrigerators used in pharmacy stock (27.0%) were aged between 8 and 10 years, while those used in vaccination programs were less than 4 years. Regular calibration of refrigerator and temperature monitoring device (TMD) was 39.0% and 24.0%, respectively. Most respondents, 44 (80.0%), knew the proper cold chain storage. However, few identified the impact of storing cold chain products with vaccines at 16 (29.1%). The transportation of cold chain products from two central medical stores assessed showed inefficiencies as only one of them uses temperature data loggers during transportations of the products mentioned above.ConclusionsThe medicines cold chain storage conformity investigated in seven districts of the Eastern Province in Rwanda was better than reported previously in other LMICs. However, cold chain storage for pharmacy stock often did not meet the requirements. The observed drawback represented a serious risk to public health. Calibrating cold chain equipment, regular maintenance, and commissioning new cold chain equipment should be done to improve cold chain storage.

The effect of dead volumes on the performance of magnetic refrigerators

Regenerative magnetic refrigeration at room temperature has the potential to overcome various problems affecting vapor compression devices while providing competitive performance, but the effects of several loss mechanisms must be evaluated and accounted for. In actual devices, inactive sections in the regenerator originate dead volumes leading to possible non-optimal exploitation of the magnetocaloric material and the associated loss mechanism. While magnetic refrigeration gained attention, few studies have systematically investigated the effects of dead volume on system performance. In this work, a one-dimensional model valid for a generic magnetic refrigerator device (either linearly reciprocating or with continuous, or discontinuous, rotary motion) is used to study the effect of the dead volume. The device performance was assessed by comparing the characteristic curves (cooling power, and COP) of an ideal device (zero dead volume) to the corresponding characteristic curves for different dead volume ratios. The performance is negatively affected if the device is operated under the same working conditions and control parameter settings used in the ideal device. This effect is higher for higher temperature spans. Nevertheless, the device could approximate the ideal performance by adjusting its control parameters. The main measures to mitigate the negative effects of dead volumes can be summarized in the necessity to operate at lower frequencies, higher fluid mass flow rates, and higher torque. The results of this study prove that the proper control of such operative parameters is able to maximize the device performance and mitigate the performance losses due to the dead volume effects.

Fracture properties of La(Fe,Mn,Si)13 magnetocaloric materials

La(Fe,Mn,Si)13 alloys are a promising material family for magnetic refrigeration. Challenges associated with their structural integrity during device assembly and operation requires deep understanding of the mechanical properties. Here we developed a workflow to quantitatively study the fracture properties of La(Fe,Mn,Si)13 plates used in magnetic cooling devices. We employed microstructural characterisation, optical examination of defects, and four-point bending tests of samples with known defect sizes to evaluate their mechanical performance. We established the residual strength curve which directly links observed defects to mechanical strength. The estimated fracture toughness KC of hydrogenated La(Fe,Mn,Si)13 is approximately 4 MPa·m1/2 for the geometry employed. The established relationship between strength and crack length enables the prediction of mechanical performance through examination of defects via optical microscopy, therefore can be used industrially for directing plate selection to guarantee the mechanical stability of refrigeration devices.

Performance Study of Portable Semiconductor Refrigeration Device Based on CFD Simulation.

Since the summer of 2022, the whole world has suffered the abnormal weather phenomena of high ambient temperature. Equipment for refrigeration, particularly portable refrigeration equipment, is crucial for personal protection in high-temperature environments, but cooling performance and miniaturization have been challenging issues. A portable air conditioner based on a semiconductor refrigeration device for human body cooling was developed. The total weight of the device is 450 g. The overall power consumption of the device is 82 W and the energy consumption ratio of semiconductor cooling plate is 0.85. The semiconductor refrigeration technology is based on the Peltier effect, supplemented by a DC fan to send the cooling air out to a specified position or zone. The structural parts are manufactured by 3D printing technology to make the overall size of the device more compact. The air volume and cooling performance of the device were analyzed by computational fluid dynamics simulation and the temperature distribution was measured by an infrared thermal imager and other instruments, and the measured results agreed with the CFD simulation results. The test ambient temperature was 20 °C. The measurement results showed that the wind speed of the hot air outlet was 6.92 m/s and that of the cold air outlet was 8.24 m/s. The cold air surface temperature reached a stable state of 13.9 °C in about 4 min, while the hot air surface temperature reached a stable state of 47.2 °C.

All-d-Metal Heusler Alloys: A Review

Heusler alloy research has increased considerably in recent years. This is mostly due to their strong desire to develop future smart device applications. However, many limiting variables remain for researchers to overcome in order to enhance their functional properties. The poor mechanical properties of these alloys restrict their use as solid-state cooling materials in magnetic refrigeration devices. A promising strategy, resulting in novel compounds with better mechanical properties and substantial magnetocaloric effects, is favoring the d–d hybridization with transition-metal elements to replace p–d hybridization. The term given to these materials is “all-d-metal”. In light of recent experimental results of the magnetocaloric effect and the increased mechanical characteristics in these alloys (with complex crystallographic behavior due to off-stoichiometry and disorder), a review of this advanced functional behavior is offered. Moreover, the impact of the substitution of transition metal for the p-group to increase mechanical ductility and considerable magnetocaloric effects has also been addressed. These Heusler alloys are a potential new class of materials for technological applications because of their optimum functional behavior. Finally, we highlighted the potential challenges and unsolved issues in order to guide future studies on this topic.

Global sensitivity analysis of a generator-absorber heat exchange (GAX) system’s thermal performance with a hybrid energy source: An approach using artificial intelligence models

• Temperature, heat and flow measurements of an experimental GAX cycle. • Evaluation of artificial intelligence (AI) techniques for multivariate modeling. • Artificial neural networks represent the GAX system with the best accuracy. • AI model coupled to the PAWN method for a global sensitivity analysis of GAX cycle. • COP is affected the most by the temperature measured at the generator inlet. Generator-absorber heat exchange (GAX) systems represent a promising alternative to substitute environmentally harmful refrigeration devices based on conventional vapor compression, as long as a proper analysis of thermal performance and the complex interactions of heat transfer that occur into GAX cycle is taken in consideration. In this research, a cooling process based on a GAX system that uses ammonia-water working fluid and a hybrid source (natural gas-solar) is studied to analyze the variables that affect the system’s thermal performance. The work’s novelty is the hybridization between artificial intelligence (AI) modeling and the global sensitivity analysis (GSA) developed with the PAWN method. Experimental data was obtained from a system with a cooling capacity of 10.5 kW (3 Ton), designed to work at heat source temperatures of 200 °C. The measured variables were the temperatures at generator, heat at evaporator, and working fluid volumetric flow. Three AI techniques (artificial neural networks, genetic programming, and support vector machines) were evaluated for modeling the thermodynamic cycle. Results obtained from the PAWN method applied to the artificial neural network, since it was the best AI model, indicates that the operational parameters with a greater impact in the system’s performance are the inlet temperature at the generator (30.7 %) and the heat measured at the evaporator for NH 3 (27.4 %), for the first output COP N H 3 . For the second output COP H 2 O , the inlet temperature at the generator (32.5 %) and the and heat measured at the evaporator for H 2 O (26.7 %), have a greater impact for such output. The proposed IA-GSA methodology contributes to the development of operational decision-making related to instrumentation, operation performance, and corrective and/or preventive maintenance actions of GAX systems. The developed thermal performance model has potential for implementation in embedded systems (smart sensors) as a critical element in control and optimization strategies to improve the performance of these cycles.

First-principles calculations to investigate structural, electronic, optical, thermoelectric, magnetic, and magnetocaloric properties of the orthochromite EuCrO3

A comparative study of the structural and electronic properties of the orthorhombic and cubic structure of EuCrO3 has been performed in this manuscript. The stability of the orthorhombic structure with respect to the cubic one has been studied. The calculated optical band gap energies were determined to be 2.09 eV, 1.95 eV and 2.02 eV along the [100], [010], and [001] directions, respectively, and are in good agreement with previous work. The studied material exhibits the behavior of a P-type semiconductor. EuCrO3 is a Gy-antiferromagnetic semiconductor with a partial magnetic moment of 2.18 µB induced by the 3d3 orbital of Cr3+ electrons and a Neel temperature of 195 K. This behavior is attributed to the super-exchange mechanisms between Cr3+-Cr3+ cations via O2– ions. Optical, thermoelectric and magnetocaloric studies revealed that europium chromite EuCrO3 is a promising candidate for photovoltaic, thermoelectric, and magnetic refrigeration devices.

Opportunities beyond CO2 for climate mitigation

Opportunities beyond CO2 for climate mitigation

Fault analysis and troubleshooting of nitrogen supply system for a ship’s nitrogen generator

This paper introduces the working principle and system work flow of the marine nitrogen generator. Emphasis is laid on the air pretreatment subsystem, nitrogen membrane separation subsystem and automatic control system of the nitrogen generator. In view of the automatic alarm shutdown fault of a ship’s nitrogen generator in the course of operation, the reason is analyzed, and it is found that the refrigeration device fault of the nitrogen generator leads to the excessive air temperature before the film inlet group, thus causing the failure shutdown. Finally, the fault location and troubleshooting are carried out.

Room-temperature polymer-assisted additive manufacturing of microchanneled magnetocaloric structures

Magnetic refrigeration is an energy-efficient, sustainable, environmentally-friendly alternative to the conventional vapor-compression cooling technology. There are several magnetic refrigerator device designs in existence today that are predicted to be highly energy-efficient, on condition that suitable working materials can be developed. This challenge in manufacturing magnetocaloric devices is unresolved, mainly due to issues related to shaping the mostly brittle magnetocaloric alloys into thin-walled channeled regenerator structures to facilitate efficient heat transfer between the solid refrigerant and the heat exchange fluid in an active magnetic regenerator (AMR) cooling device. To address this challenge, a novel extrusion-based additive manufacturing (AM) method has been developed to 3D print microchanneled magnetocaloric structures. The printing ink consists of magnetocaloric powders, a polymer binder, and multiple solvents to achieve desirable shear-thinning property, which is critical for a robust printing process. Acting as a sacrificial binding agent for the magnetic powders, the polymer binder holds the 3D printed structures in place and is removed subsequently using a two-step heat-treatment process. To demonstrate the effectiveness of the fabrication process, spatially designed microchannels with minimum dimensions of 150 µm were achieved using nanoscaled La 0.6 Ca 0.4 MnO 3 powders (diameter~10 nm). Results indicate that the crystallographic properties and magnetofunctional response of the sintered 3D printed samples are comparable to that of the precursor powders. Overall, this study provides a promising route for realizing low-cost magnetic regenerators, thus potentially eliminating one of the main barriers to the commercialization of magnetic cooling technology. • Room temperature extrusion-based method for 3D printing magnetocaloric structures. • Significant magnetocaloric response in 3D printed LCMO scaffolds (ΔS=4.9 J/kg-K at 5 T). • Microchanneled magnetocaloric structures with record spatial resolution (dia∼150 µm). • Overcoming a crucial barrier to the commercialization of magnetic cooling technology.

Modeling thermoelectric effects in piezoelectric semiconductors: New fully coupled mechanisms for mechanically manipulated heat flux and refrigeration

We present a continuum theory for analyzing the interaction between the thermoelectric and mechanical fields in piezoelectric semiconductors. The balance laws and dissipation inequality are formulated in the reference configuration. Thermodynamically consistent constitutive equations are derived, including the drift-diffusion current, Fourier's law for thermal flux, Seebeck effect, and Peltier effect, by introducing a generalized Fick's law. The heat conduction equation and Joule heating generation with the semiconducting effect are derived by combing the energy balance and the second Gibbs relation. The framework is then geometrically linearized for applications in small deformation of crystal solids. Based on the newly developed framework, two new coupling mechanisms between thermoelectric and mechanical fields in crystals of class of 6mm are identified. 1) A mechanical load can block both electron and thermal fluxes in the loading area via the mechanically induced potential well. At a strain level of 1%, the current and heat flow can be reduced by as much as 80%. This effect facilitates the design of new switching devices. 2) The mechanical load can surprisingly act as a current amplifier through the induced potential barrier. Furthermore, making use of the new and unusual Joule heating generation, thermal dipoles can be created, indicating that mechanical loading can lead to local refrigeration. Via a simple numerical model, we demonstrate that the mechanical deformation can produce a temperature difference of 0.06 K at the strain level of around 1%. Based on this new and exciting cooling mechanism, we further propose a novel multi-stage pyramidal cascade device for refrigeration. The framework in this paper provides a foundation for analyzing multiple physics problems in semiconductor structures and also potential ideas for switching and refrigeration devices. Since it is based on finite deformation theory, the present framework would be helpful in analyzing the behavior of emerging flexible semiconductor materials or developing the corresponding computational methods.

High performance of carbon nanotube elastocaloric refrigerators over a large temperature span

Compression of greenhouse gases still dominates the market of refrigeration devices. Although well stablished and efficient, this technology is neither safe for the environment nor able to be scaled down to nanoscale. Solid-state cooling technologies are being developed to overcome these limitations, including studies at nanoscale. Among them, the so-called elastocaloric effect (eC) consists of the thermal response, $\Delta T$, of a material under strain deformation. In this work, fully atomistic molecular dynamics simulations of the eC in carbon nanotubes (CNTs) are presented over a large temperature span. The efficiency of the CNTs as solid refrigerators is investigated by simulating their eC in a model of refrigerator machine running under Otto-like thermodynamic cycles (two adiabatic expansion/contraction plus two isochoric heat exchange processes) operating at temperatures, $T_\mbox{O}$, ranging from 300 to 2000 K. The coefficient-of-performance (COP), defined as the ratio of heat removed from the cold region to the total work performed by the system per thermodynamic cycle, is calculated for each value of $T_\mbox{O}$. Our results show a non-linear dependence of $\Delta T$ on $T_\mbox{O}$, reaching a minimum value of about 30 K for $T_\mbox{O}$ between 500 and 600 K, then growing and converging to a linear dependence on $T_\mbox{O}$ for large temperatures. The COP of CNTs is shown to remain about the same and approximately equal to 8. These results are shown to be weakly depend on CNT diameter and chirality but not on length. The isothermal entropy change of the CNTs due to the eC is also estimated and shown to depend non-linearly on $T_\mbox{O}$ values. These results predict that CNTs can be considered versatile nanoscale solid refrigerators able to efficiently work over a large temperature span.

Giant room-temperature electrocaloric effect within wide temperature span in Sn-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free thin films

The electrocaloric (EC) effect cooling technique of environmentally friendly lead-free thin film materials driven by electric fields has recently gained tremendous attention due to the urgent demand for microelectronic and integrated circuit refrigeration devices. However, the widespread use of lead-free materials in EC devices is seriously hindered due to the small electrocaloric temperature change (ΔT) within a narrow operation temperature span (Tspan) near room temperature. Here, lead-free Ba0.85Ca0.15Zr0.1Ti0.9-xSnxO3 (BCZT-xSn, 0 ≤ x ≤ 0.03) thin films were prepared on substrates (Pt/Ti/SiO2/Si) via a sol-gel route. The BCZT-0.02Sn thin film presents an excellent EC effect (ΔT = 32.74 K, ΔS = 37.18 J kg−1 K−1) and large EC strength (ΔT/ΔE = 0.033 K cm kV−1, ΔS/ΔE = 0.037 J cm K−1 kg−1 kV−1) over a wide Tspan (∼26 K) under 1000 kV cm−1 near room temperature. The giant ΔT is mainly attributed to the emergence of an intermediate O phase and the formation of a multiphase (R, O and T phases) coexistence structure at room temperature, while the diffuse phase transition behavior is responsible for the wide Tspan. Our study provides a new idea for developing environment-friendly EC materials with an excellent room-temperature ΔT over a broad operational temperature region.

Direct Measurement of the Magnetocaloric Effect through Time-Dependent Magnetometry

The magnetocaloric effect of a given material is typically assessed through indirect estimates of the isothermal magnetic entropy change, $\mathrm{\ensuremath{\Delta}}{S}_{M}$. While estimating the adiabatic temperature difference, $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$, is more relevant from the standpoint of refrigeration device engineering, this requires specialized experimental setups. We here present an approach to directly measure $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ through time-dependent magnetometry in a commercial superconducting quantum interference device (SQUID) device. We use as reference material gadolinium under a 20-kOe field change, and compare our results with those of the literature. Under nonadiabatic experimental conditions, a remarkably similar $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}(T)$ curve profile is obtained; however, its peak amplitude is underestimated. With a simple compensation methodology we are able to further approximate the profile of the $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}(T)$ curve obtaining the peak amplitude, the maximizing temperature, and the FWHM within relative errors of $\ensuremath{-}4\mathrm{%}$, $\ensuremath{-}0.7\mathrm{%}$, and 11%, respectively. Our reported approach makes the measurement of both $\mathrm{\ensuremath{\Delta}}{S}_{M}(T)$ and $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}(T)$ possible with a single instrument, enabling accelerated progress towards new, competitive, and industry-ready materials.

Influence of capillary tube length on the performance of domestic refrigerator with eco-friendly refrigerant R152a

The household heating and cooling system often use the capillary device. The use of the helical capillary eliminates the need for lightweight refrigeration devices in the system. Capillary pressure is noticeably affected by the capillary geometric parameters, such as length, mean diameter, and pitch. This paper is concerned with the effects of the capillary length on the performance of the system. Three separate length capillary tubes were used in the experiment. The data on R152a were studied under various conditions to assess the impact of varying the length. Maximum COP is obtained at an evaporator temperature of − 12 °C and capillary length of 3.65 m. The result is drawn that the system performance enhances when the capillary length is improved to 3.65 m when compared to 3.35 m and 3.96 m. As a result, as the capillary length increases up to a specific amount, the system's performance improves. The findings from the experiment were compared with those from the computational fluid dynamics (CFD) analysis.

A REVIEW OF MECHANOCALORIC REFRIGERATION DEVICES FROM 2012 TO 2020

Solid-State room temperature refrigeration devices have been reported extensively in the last decades with a focus on magnetocaloric effect materials, a thermal response to an applied magnetic field in a solid refrigerant. Currently, the limitations to generate large magnetic fields needed for better efficiencies have posed a challenge to rival current standard vapor compression cycles. Conventional refrigerants in standard vapor cycles are expected to contribute to global warming close to 25000 kgCO2,eq over the next 100 years. The need to overcome such challenges has driven a search for alternative i-caloric effects such as electrocaloric which is the thermal response of the material to the application of an electric field and mechanocaloric, a thermal response to the application of a stress field. Recently, the latter effect is being reported and categorized by the type of stress field applied. They are named elastocaloric for uniaxial stress, barocaloric for isostatic stress, and torsiocaloric for pure shear. Due to its simple stress, elastocaloric regenerators with shape memory alloys (SMA) were reported first. With a design similar to shell-tube heat exchanger with SMA being the shell and tubes while the heat transfer fluids (HTF) flows within the tubes. Promising thermodynamic cycle parameters such as coefficient of performance COP 11.0 with a temperature span of 24.6 K subject to a strain of 4.5% have been achieved with this design. Another device was reported working in a continuous non-regenerative manner with steady state being reached within seconds presented COP of 9.5 and a heat load of 250 W for a temperature span of 10K. As for barocaloric materials some researchers announced that are currently developing devices with these phenomena. Its main challenge is to elaborate a design that allows cyclic isostatic stress application, usually achieved by encapsulating the barocaloric material. One research group presented a study on a simulated active barocaloric regenerator on metal alloys and Acetoxy Silicone Rubber (ASR). The most recent mechanocaloric effect is the torsiocaloric. Two devices for measuring the torsiocaloric effect where presented, one in a batch form and another setup similar to a heat exchanger shell-tube where the tube is the solid-state refrigerant that can be twisted while in direct contact with the HTF flowing on the shell side. Thus, we aim to provide an in-depth analysis of recent studies of mechanocaloric devices describing their working cycles, thermodynamic parameters, HTF circuits and comparing their design choices, and forecast the design of near future mechanocaloric solid-state devices.

Synthesis, structural and physical properties of ABO3 based hexagonal polytypes: A review and discussion

The aim of this review paper is to provide the compact overview of experimental synthesis route, crystallography of perovskite (ABO3) hexagonal polytypes and their related physical properties. Structural stacking sequence of the oxygen deficient hexagonal perovskite oxides (ABO3-δ) is briefly discussed. The fundamental aspects of magnetic and electrical properties involved in hexagonal polytypes are elaborated using reported systems. The magnetic field induced effect such as magnetocaloric effect, magnetoresistance and magneto-dielectric effect in perovskite hexagonal polytypes are also discussed for their possible application in magnetic refrigeration, magnetic sensors and memory devices.