Low-Temperature Preparation of High-Quality Lanthanum Hydride at Ambient Pressure: Pathway Screening and Experimental Scheme Based on Constraint Network Dynamics Catalysis Theory

After the realization of high-temperature superconductivity in lanthanum hydride under high pressure, ambient pressure preparation has become a key challenge in this field. Traditional pure thermal hydrogenation methods require temperatures above 250°C, with hydrogen atom infiltration rates of only about 50%, poor product crystal regularity, and inability to meet the requirements of superconducting applications. Based on the catalysis theory of constraint network dynamics, this paper screens three optimal pathways from nine candidate catalytic pathways through large-scale computer simulations: sodium catalysis (180°C, hydrogen infiltration rate 85.0%, purity grade A), cerium homologous doping catalysis (200°C, hydrogen infiltration rate 83.7%, purity grade S), and hydrostatic pressure lattice pre-distortion catalysis (160°C, hydrogen infiltration rate 87.5%, purity grade S). After thermodynamic self-consumption screening, potassium and lithium were eliminated due to spontaneous chemical reaction with hydrogen within the reaction temperature range. The 250°C pure thermal hydrogenation pathway was eliminated due to its C-grade purity. Three pathways, namely two-dimensional interfacial confinement, plasma activation, and neutron energy injection, were temporarily set aside due to application scenarios or equipment barriers. This paper provides detailed experimental operation guides for the three optimal pathways, and proposes three mild superconducting excitation schemes (thermal pulse, microwave irradiation, neutron irradiation) as a complete set. The prepared lanthanum hydride material contains a high density of excitable neutron pairs internally, and can generate zero-resistance current through mild external energy triggering. All preparation conditions are at ambient or low pressure, with temperatures not exceeding 210°C, requiring no ultra-high pressure equipment, and are fully operable in conventional laboratories. This provides a complete pathway from theoretical screening to experimental verification for the engineering preparation of lanthanum hydride superconducting materials.