Houbo Zhou's research while affiliated with Chinese Academy of Sciences and other places

The environmental friendliness and high efficiency of magnetocaloric refrigeration make it a promising substitute for vapor compression refrigeration. However, the common use of heat transfer fluid in conventional passive magnetic regenerators (PMRs) and active magnetic regenerators (AMRs) makes only partial materials contribute to the regeneration process, which produces large regeneration loss and greatly limits the regeneration efficiency and refrigeration performance at high frequency. Herein, we propose a new conceptual hybrid magnetic regenerator (HMR) composed of multiple solid-state high thermal conductivity materials (HTCMs) and magnetocaloric materials (MCMs), in which both HTCM and MCM elements participate in the regeneration process. This novel working mode could greatly reduce regeneration losses caused by dead volume, pressure losses, and temperature nonuniformity in heat transfer substances to markedly improve regeneration efficiency at high working frequencies. Using the experimentally obtained adiabatic temperature change and magnetic work and with the help of finite element simulation, a maximum temperature of 26 K, a dramatically large cooling power of 8.3 kW/kg, and a maximum ideal exergy efficiency of 54.2% are achieved at the working frequency of 10 Hz for an ideal prototype device of a rotary HMR magnetocaloric refrigerator, which shows potential for achieving an integrative, advanced performance against current AMR/PMR systems.

It is well known that the epitaxial strain plays a vital role in tuning the magnetic states in transition metal oxide LaCoO3 films. Here, we reported a robust long-range ferromagnetic (FM) ground state in a tensile-strained perovskite LaCoO3 film on a SrTiO3 (STO) substrate, which has a very significant attenuation when the thickness ranges from 10 to 50 nm. It is speculated that such attenuation may be caused by the appearance of the cross-hatched grain boundary, which relaxes the tensile strain around the crosshatch, resulting in the local non-FM phases. Magnetic force microscope observation reveals non-FM patterns correlated with the structural crosshatches in the strain-relaxed film even down to a temperature of 2 K and up to a magnetic field of 7 T, suggesting the phase separation origin of magnetization attenuation. Furthermore, the investigations of the temperature-dependent inverse magnetic susceptibility show a deviation from the Curie–Weiss law above the transition temperature in a 50-nm-thick LaCoO3/STO film but not in the LaCoO3/LaAlO3 film, which is ascribed to the Griffiths phase due to the crosshatch-line grain boundaries. These results demonstrated that the local strain effect due to structural defects is important to affect the ferromagnetism in strain-engineered LaCoO3 films, which may have potential implications for future oxide-based spintronics.

Pentagonal-ring-structured PtP2 bulk crystals and the two-dimensional (2D) PtP2 with rich theoretical physical and chemical properties have attracted considerable attention for the applications in high-performance electronic and optoelectronic devices. Here, high-quality PtP2 single crystals have been successfully prepared by using a tin flux method with the optimal molar ratios of Pt and P. 3D weak localization effect and negative magnetoresistance (NMR) are observed in the high-quality PtP2 single crystals for the first time. Crystalline structure, magnetization, and optical spectral characterizations have demonstrated that the defects in PtP2 crystals can suppress the NMR effect and magnetic ordered states. These findings open up a way to synthesize the bulk and low-dimensional noble-metal-based phosphides of high quality and provide new platforms for studying the different correlated electronic states.

The barocaloric effect (BCE) has emerged as an intense research topic in regard to efficient and clean solid-state refrigeration. Materials with solid-liquid phase transitions (SL-PTs) usually show huge melting entropies but cannot work in full solid-state refrigeration. Here, we report a colossal barocaloric effect realized by exploiting high entropy inherited from huge disorder of liquid phase in amorphous polyethylene glycol (PEG), which is solidified by introducing 5 wt.% polyethylene terephthalate (PET). Transmission electron microscopy (TEM) combined with X-ray diffraction (XRD) demonstrates the amorphous nature of the high-temperature phase after fixation by PET. Although PEG loses its –OH end mobility in amorphous solid, high entropy still retains owing to the retained high degrees of freedom of its molecular chains. The remaining entropy of amorphous PEG is up to 83% of that of liquid PEG in PEG10000/PET15000, and the barocaloric entropy change reaches ΔSp ∼ 416 J·kg⁻¹·K⁻¹ under a low pressure of 0.1 GPa, which exceeds the performance of most other BCE materials. Infrared spectra combined with density function theory (DFT) calculations disclose conformational change from the liquid to amorphous state, which explains the origin of the large entropy retained and hence the colossal BCE of the solidified PEG. This research opens a new avenue for exploring full solid-state barocaloric materials by utilizing genetic high entropy from huge disordering of liquid phases in various materials with SL-PTs.

Strongly correlated electron materials that exhibit rich phase transition and multiple phase separation have shown many fascinating properties. Using these properties in the electronic device will require the ability to control their phase transition and phase separation behaviours. In this work, we report a sensitive electric field control of firstorder phase transition in epitaxial (011)-Nd 0.5 Sr 0.5 MnO 3 /0.71Pb(Mg 1/3 Nb2/3 )O 3 -0.29PbTiO 3 (PMN-PT) heterostructure. The pristine film shows phase separation character with the penetration of the ferromagnetic metallic phase into the charge and orbital ordered antiferromagnetic insulating phase in the pristine film, and this was revealed by the XMCD and XLD investigation. The (011)-oriented PMN-PT piezoelectric single crystal adopted can exert anisotropic in-plane tensile strains on the epitaxial Nd 0.5 Sr 0.5 MnO 3 film when applying the electric field. The coaction of the electric field-induced strain and polarization effects of the PMN-PT piezoelectrics enable the efficient manipulation of orbital ordering and the coupled electronic and magnetic phase transitions. Accordingly, a small +1.6 kV cm -1 electric field can recover the first-order metal-insulator transition which was inhibited in the pristine heterostructure, increase the transition temperature by 56 K and the maximum resistance change reaches 7033%. Furthermore, the electric field demonstrated nonvolatile control of magnetization, and the magnetoelectric coefficient reaches 1.89*10-7 sm -1 at 200 K. This work indicates that choosing the piezoelectric substrate with appropriate electric-field-induced strain opens a route to designing functional electronic devices where the tunable macroscopic properties derive from strongly interacting degrees of freedom present in the manganite

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoOx films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co-O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

Barocaloric effect (BCE) has emerged as one of intense topics aiming at solid-state refrigeration featuring efficiency and cleanness. Materials with solid-liquid phase transition (SL-PT) usually show huge melting entropy but cannot work in full solid-state refrigeration. Here we report colossal barocaloric effect realized by exploiting high entropy inherited from huge disorder of liquid phase in amorphous polyethylene glycol (PEG), which is solidified through introducing 5wt.% polyethylene terephthalate (PET). TEM combined XRD demonstrate the amorphous nature of high-temperature phase after fixed by PET. Although the PEG loses the -OH end mobility in amorphous solid, high entropy still retains owing to retained high freedom of molecule chains. The remained entropy in amorphous PEG is up to 83% of liquid PEG in PEG10000/PET15000, and the barocaloric entropy change reaches ΔS p ∼ 416 J·kg − 1 ·K − 1 under a low pressure 0.1 GPa, which exceeds the performance of most other BCE materials. Infrared spectra combined with density function theory (DFT) calculations disclose conformational change from liquid to amorphous state, which explains the origin of huge entropy retained and hence colossal BCE in the solidified PEG. This research opens a new avenue for exploring full solid-state barocaloric materials by utilizing genetic high entropy from huge disordering of liquid phase in various materials with SL-PT.

We report the enhancement of the thermal conductivity of neopentylglycol (NPG) by compositing it with graphene nanosheets (GPNs). Adding 50 wt% GPNs enhanced the thermal conductivity from 0.42 to 18.4 Wm⁻¹K⁻¹, and the barocaloric entropy change can still reach 122 Jkg⁻¹K⁻¹ under pressure loading of 0 → 1.0 kbar. The obtained composites demonstrated reduced thermal hysteresis, which will facilitate the large reversible entropy change. The present work thus provides a simple and feasible way to enhance the thermal conductivity of plastic crystals with a giant barocaloric effect, and promisingly accelerate the application of these materials in the solid-state refrigeration technique.

Solid-state refrigeration based on the caloric effect is viewed as a promising efficient and clean refrigeration technology. Barocaloric materials were developed rapidly but have since encountered a general obstacle: the prominent caloric effect cannot be utilized reversibly under moderate pressure. Here, we report a mechanism of an emergent large, reversible barocaloric effect (BCE) under low pressure in the hybrid organic–inorganic layered perovskite (CH 3 –(CH 2 ) n −1 –NH 3 ) 2 MnCl 4 ( n = 9,10), which show the reversible barocaloric entropy change as high as Δ S r ∼ 218, 230 J kg ⁻¹ K ⁻¹ at 0.08 GPa around the transition temperature ( T s ∼ 294, 311.5 K). To reveal the mechanism, single-crystal (CH 3 –(CH 2 ) n −1 –NH 3 ) 2 MnCl 4 ( n = 10) was successfully synthesized, and high-resolution single-crystal X-ray diffraction (SC-XRD) was carried out. Then, the underlying mechanism was determined by combining infrared (IR) spectroscopy and density function theory (DFT) calculations. The colossal reversible BCE and the very small hysteresis of 2.6 K (0.1 K/min) and 4.0 K (1 K/min) are closely related to the specific hybrid organic–inorganic structure and single-crystal nature. The drastic transformation of organic chains confined to the metallic frame from ordered rigidity to disordered flexibility is responsible for the large phase-transition entropy comparable to the melting entropy of organic chains. This study provides new insights into the design of novel barocaloric materials by utilizing the advantages of specific organic–inorganic hybrid characteristics.