1：Experimental Design and Method Selection:

The LAB ceramic samples were prepared using a traditional solid-state reaction method. The rationale was to synthesize a composite with specific molar ratios to achieve desired dielectric properties and low shrinkage. Theoretical models included phase transformation analysis and dielectric property calculations using the Clausius-Mossotti equation.

2：Sample Selection and Data Sources:

High-purity powdered samples of Li2CO3 (≥98%), Al2O3 (≥99%), and H3BO3 (≥98.5%) were obtained from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. The selection criteria were based on purity to ensure accurate composition.

3：5%) were obtained from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. The selection criteria were based on purity to ensure accurate composition. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included an X-ray diffractometer (Model X’Pert PRO, PANalytical), scanning electron microscope (Model: JSM6380-LV SEM, JEOL), thermal dilatometer (DIL402C, Netzsch), network analyzer (E5071C, Agilent Co.), and ball milling apparatus with zirconia balls. Materials were Li2CO3, Al2O3, H3BO3, alcohol, polyvinyl alcohol (PVA), and silver powder for co-firing tests.

4：Experimental Procedures and Operational Workflow:

Powders were weighed according to Li2CO3:Al2O3:H3BO3=1:1:4, mixed for 4 h with zirconia balls in alcohol at 250 r/min, dried, calcined at 600°C for 4 h, ball milled again, granulated with 5 wt% PVA, pressed into cylinders under 200 MPa, heated to 550°C to remove PVA, and sintered at 675–750°C for 4 h. Characterization involved XRD, SEM, density measurement, shrinkage measurement, and microwave dielectric property testing.

5：Data Analysis Methods:

Data were analyzed using XRD for phase identification, SEM for morphology, Archimedes method for density, thermal dilatometer for shrinkage, and network analyzer with TE01δ method for dielectric properties. Statistical analysis included calculating shrinkage using formula (1) and τ? using equation (2).