Negative temperature coefficient thermistor (NTC) is widely used in temperature measurement field, especially in the temperature range from 0 °C to 40 °C. For its strong nonlinearity, NTC should be calibrated in this temperature range with three or more temperature fixed points. However, in this temperature range, there are only two defined temperature fixed points in ITS-90: Gallium point and water triple phase point. In this paper, a phenol temperature fixed point was developed to make up the deficiency. Melting and freezing temperature curves are studied for the single-component phenol in a conventional size cell. The phenol melting plateau can last for more than 10 h with melt range of less than of 100 mK. The freezing plateau can last approximately 4 h with the observed temperature variation less than 5 mK within 2 h, which showed a high degree of reproducibility. Different methods were employed to accurately determine the phase transition temperature. By repeatedly realizing phenol melting plateaus and freezing plateaus, the melting point temperature was determined to be 40.6109 °C ± 0.074 °C (k = 2) with a reproducibility of less than 8.3 mK, and the freezing point temperature was 40.6348 °C ± 0.072 °C (k = 2), with a reproducibility of less than 1.6 mK. The results showed that the phenol freezing point temperature is the most suitable temperature reference standard near 40.6 °C.

负温度系数热敏电阻（NTC）广泛应用于温度测量领域，特别是在0℃至40℃的温度范围内。由于NTC具有很强的非线性，因此应在该温度范围内用三个或更多温度固定点进行校准。然而，在这个温度范围内，ITS-90中只有两个定义的温度固定点：镓点和水三相点。本文提出了苯酚温度固定点来弥补这一不足。研究了传统尺寸电池中单组分苯酚的熔化和凝固温度曲线。苯酚熔融平台可持续10小时以上，熔融范围小于100 mK。冷冻平台可持续约4小时，2小时内观察到的温度变化小于5mK，表现出高度的重现性。采用不同的方法来准确测定相变温度。通过反复实现苯酚熔化平台和冷冻平台，确定熔点温度为40.6109℃±0.074℃(k=2)，重现性小于8.3mK，凝固点温度为40.6348℃±0.072 °C (k = 2)，重现性小于 1.6 mK。结果表明，苯酚冰点温度在40.6℃附近是最合适的温度参考标准。