Caloric Effects in Bulk Lead‐Free Ferroelectric Ceramics for Solid‐State Refrigeration

Abstract

[a] Thec aloric behavior of bulk (Ba 0.865 Ca 0.135 Zr 0.1078 Ti 0.8722 Fe 0.01 Nb 0.01 )O 3 (BCZTO-FeNb) with respecttomultiplep hysical inputs is investigated. Predictions were made by using modified Maxwells relationsi nc onjunction with independent experimental data. BCZTO-FeNb possesses significant potential for multiple caloric effects.A peak electrocaloric effect of 0.5 K( 307 K) was predictedf or electric fields of 0-3 kV mm À1,s ignificantlyh igher than for other BCZTO-based compositions.Amaximum elastocaloric cooling of 1.17 K( 298 K) was achievedf or an applied stress of 0-200 MPa( 3kVmm À1). Finally,anew component of the electric-field-driven caloric effect is reported as the inverse piezocaloric effect, with am aximumt emperature changeo f 0.4 K( 298 K).Ferroelectric materials have recently acquiredg lobal attention owing to their emerging potential as solid-state refrigerants. [1][2][3][4][5] When ferroelectric materials are subjected to an external electricf ield in an adiabatic manner, at emperature changei si nduced. This effect is known as the electrocaloric effect (ECE) and has garneredt he attention of researchers worldwide.[2-4, 6-11] TheE CE is one of many caloric effects that are now being rigorously investigated with the aim of developingnew refrigeration technologies. [6,9,[12][13][14][15][16] These caloric effects have been proposed as ac redible solution to the growingd emand for cleaner, more efficient, ecofriendly,a nd miniaturized devices for space-cooling applications. [12,13,16] Thed evelopment of caloric-effect-based solid-state coolers will usher in an ew era of compact, mobile,a nd highly responsive refrigerators capable of onboard installation and powered by ambient or waste energy. [8,9,13,16,17] This will help mitigate the drawbacks associated with vapor-compression technology,w hich currently forms the backboneo ft he commercial refrigeration industry.ECE is amajor contender because it promises quiet operation, options for energy recovery,h igh efficiency,l ong lifespans,a nd cleaner operation. [12,13,16] However, the currenta pproach stillh as some limitations,t he major being selection of material shape or morphology. In this context, recently an umber of nanocomposite-and thin-film-based ferroelectrics have been studied for EC applications. [18][19][20][21] These are capable of aECE of ca. 30-50 K; however, the required electric field was very high (80-250kVmm À1 ;a lmost 20-80 times larger than that required for bulk ferroelectrics).[18-21] Furthermore,t hin films suffer from poor heat extractionc apacity owing to their reduced volume.[6, 10, 11] By contrast, bulk materials can provide feasible heat extraction but require high-intensity electric potentials for operation and suffer from limited (DT)v alues. [6,7,9,12,16] Theh ighest (DT)i so ften realizedn ear the ferro-para transition temperature, which limits their applicability to higher-than-room-temperature settings.[2, 6-8] Ap revious publicationp ostulated that one of the solutionst ot his problemi st od rive a...

Large barocaloric effect and pressure‐mediated electrocaloric effect in Pb0.99Nb0.02(Zr0.95Ti0.05)0.08O3 ceramics

“…However, there is still a lack of materials where multi‐ferroicity can be observed within a suitable temperature range. Notwithstanding, with contemporary advances, it is now established that ferroelectric materials enable coupling of two or more caloric effects . eCE has been reported for many bulk ferroelectric materials .…”

“…This helps to further utilize the entropy change of second‐order phase transition. This effect has been well explored to enhance the EC response in MPB materials as well as others …”

“…However, the field of multi‐caloric effect is new and only limited data is available in the published research . A ferroelectric material undergoes change in dipolar orientation (domain switching) when subjected to transient thermal or mechanical input . These materials are traditionally investigated for ECE with the largest reported value being well beyond 50 K .…”

“…Recently, eCE was also reported in ferroelectric materials and a combination of the two could be utilized to further enhance cooling capacity . For ferroelectric materials, external biasing has been reported to impart additional benefits and a higher caloric effect . Literature reveals that domain switching mechanisms (ferroelastic and ferroelectric) can be employed to tune and enhance caloric output .…”

Diesel Exhaust Emission Soot Coated Pyroelectric Materials for Improved Thermal Energy Harvesting

“…Although results are promising, still these materials are only sufficient for low power electronic devices. Large number of materials such as BaCa x Ti 1‐ x O 3 , Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 , PbZr x Ti 1‐ x O 3 , BaTi 1‐ x Sn x O 3 have been examined for energy harvesting applications . In order to improve the performance, several strategies such as inducing porosity, tuning pyroelectric coefficient, and some other physical techniques have been proposed .…”