Analyzing Temperature-Induced Phase Transitions in LK-99 (Pb₁₀₋ₓCuₓ(PO₄)₆O)

Objective—Life on Earth evolved under a rhythmic 24-hour cycle of day and night (T24). As a result, organisms possess a light-sensitive circadian pacemaker with an internal period that is close to (but not exactly) 24 h. Recent studies have demonstrated that extreme T-cycles that deviate from Earth’s photoperiod, including T7, T20, T22.5, T27, and T30, pose physiological challenges for the mammalian circadian system, affecting photoentrainment and sleep as well as physical and cognitive health. However, adaptability to less extreme T-cycles that deviate only slightly (<1 h) from T24 remains largely unexplored. One example is the Martian photoperiod of T24.66, which is relevant to space exploration missions [Barger et al. (2012) Sleep 35(10):1423–1435] and has received increasing attention from chronobiologists and astrobiologists in recent years. Here we present the first detailed investigation of the effects of T24.66 on circadian (~24 h) and ultradian (<24 h) rhythms, sleep/wake patterns, and memory performance in laboratory mice. Methods—Male and female C57BL/6J mice were housed individually in light-tight chambers that provided artificial light/dark cycles of T24 (baseline) and subsequently two weeks of T24.66 mimicking the Martian photoperiod; a within-subjects design was used. Home cage circadian locomotor activity was monitored continuously with passive infrared (PIR) sensors (n = 12). Sleep was assessed noninvasively by piezoelectric sensors (n = 4) or by cortical electroencephalography (EEG) (n = 3). Memory function was assessed using the spontaneous object recognition memory task (n = 12), which is known to be sensitive to hippocampal dysfunction as well as sleep and circadian rhythm disturbance. Results—(a) Under T24.66, the period length (τ) of daily locomotor activity increased from 24.2 h to 24.7 h without any significant change in the power of the circadian activity rhythm. This period lengthening caused activity midpoints to be delayed across days, resembling the phase delay in circadian rhythms in humans working under the Phoenix Mars Lander (PML) mission [Barger et al. (2012) Sleep 35(10):1423–1435]. (b) Fast Fourier transform (FFT) and wavelet analyses revealed an increase in the power of the ultradian activity rhythm, notably at the 8-h harmonic but not at the 6-h or 12-h harmonic. (c) Changes in daily rhythms were accompanied by increased sleep and reduced waking EEG fast θ power (8–12 Hz) in the dark phase, with a decline in memory for objects after short delays (5 min and 2 h). Conclusions—Although the Martian photoperiod only deviates slightly from T24, exposure to T24.66 alters the spectral composition of activity rhythms by amplifying ultradian noise, as well as attenuating alertness and memory function in the dark (active) phase. This lighting regime provides a promising approach to study (mal)adaptation of the mammalian circadian system to the Martian photoperiod.

Recommended citation: Yihan Wang†, Juntang Wang†, Xinze Xu, Yihen Han, Qinyi Chen, Ghulam Hussain, Xiawa Wang. (2025). "Analyzing Temperature-Induced Phase Transitions in LK-99 (Pb₁₀₋ₓCuₓ(PO₄)₆O)." 17th International conference on materials chemistry (MC17).